Nobuhito KOKUBO
| Department of Engineering Science | Associate Professor |
| Cluster III (Fundamental Science and Engineering) | Associate Professor |
| Division of General Education（School of Informatics and Engineering ） | Associate Professor |
| Division of General Education（Graduate School of Informatics and Engineering） | Associate Professor |
| Nanotribology Research Center | Associate Professor |
Researcher Information
Research Keyword
Career
- 01 Jan. 2012
電気通信大学大学院情報理工学研究科, 准教授 - 01 Sep. 2011
電気通信大学情報理工学部, 准教授 - 01 Apr. 2007 - 31 Aug. 2011
Kyushu University, Center for Research and Advancement in Higher Education, Assistant Professor - 01 Jun. 2006 - 31 Mar. 2007
Kyushu University, Center for Research and Advancement in Higher Education, Assistant Professor - 01 May 2006 - 31 May 2006
Kyushu University, Center for Research and Advancement in Higher Education, Assistant Professor - 01 Apr. 2004 - 30 Apr. 2006
University of Tsukuba, Institute of Materials Science, Assistant Professor - 01 Oct. 2003 - 31 Mar. 2004
University of Tsukuba, Institute of Materials Science, Assistant Professor - 01 Oct. 2001 - 30 Sep. 2003
Leiden University, Kamerlingh Onnes Laboratory, 博士研究員 - 01 Oct. 1999 - 30 Sep. 2001
Leiden University, Kamerlingh Onnes Laboratory, 客員研究員
Educational Background
Member History
- 01 Apr. 2022 - 31 Mar. 2024
運営指導委員, 神奈川県立相模原高等学校スーパーサイエンスハイスクール運営指導委員会, Others - 01 Apr. 2021
第77～78期代議員, 日本物理学会, Society - 16 Mar. 2021 - 19 Mar. 2021
2021年第68回応用物理学会 講演奨励賞審査委員, 2021年第68回応用物理学会 講演奨励賞審査委員, Society - 12 Mar. 2021 - 15 Mar. 2021
日本物理学会 学生優秀発表賞 領域6審査委員, 日本物理学会 学生優秀発表賞 領域6審査委員, Society, 日本物理学会 2021年第76回年次大会 - 05 Dec. 2018 - 10 Dec. 2020
幹事, ボルテックスフォーラム総会, Others - 08 Sep. 2020 - 11 Sep. 2020
日本物理学会 学生優秀発表賞 領域6審査委員, 日本物理学会 学生優秀発表賞 領域6審査委員, Society - 09 Sep. 2018 - 12 Sep. 2018
学生優秀発表賞 領域6審査委員, 学生優秀発表賞 領域6審査委員, Society - Mar. 2018
学生優秀発表賞 領域6審査委員, 学生優秀発表賞 領域6審査委員, Society - May 2009 - Apr. 2010
領域世話人（領域６）, 日本物理学会, Society
Research Activity Information
Paper
- NbTiN SQUID-on-tip fabricated by self-aligned deposition using reactive DC magnetron sputtering
N. Kokubo; B. Gerelkhuu
Applied Physics Letters, AIP Publishing, 124, 26, 262601-1-262601-5, Jun. 2024, Peer-reviwed, We fabricate superconducting quantum interference devices (SQUIDs) made of niobium-titanium nitride (NbTiN) thin films on the apex of sharp quartz capillaries. By incorporating reactive DC magnetron sputtering into the self-aligned deposition process for the SQUID-on-tip (SOT) fabrication, we produce NbTiN SOT devices with an effective diameter of ∼100 nm. The ø110 nm device has a superconducting transition temperature of 13.2 K, magnetic flux noise down to 0.7 μΦ0/Hz0.5 (4 K), and operating temperatures of 1.8–10 K. The developed technique enables the synthesis of nitride and other superconductors, thereby expanding the range of materials available for SOT devices.
Scientific journal, English - Finite-size effect of critical penetration of Pearl vortices in narrow superconducting flat rings
N. Kokubo; S. Okayasu; T. Nojima
Journal of Applied Physics, 125, 22, 223906-1-223906-6, 14 Jun. 2019, Peer-reviwed, © 2019 Author(s). We revisit the critical penetration of Pearl vortices in narrow superconducting flat rings cooled in magnetic fields. Scanning superconducting quantum interference device microscopy measurements showed how a magnetic field penetrates and vortices are trapped in flat rings made of amorphous MoGe thin films. Counting the number of trapped vortices for each image, we found that the vortices are completely excluded from the ring annulus when the applied field H is below a threshold field H p: Above this field, the vortices increase linearly with the field. The obtained values of H p depend on the annulus width w ring and follow the relation μ 0 H p = (1.9 ± 0.1) φ 0 / w ring 2 with the superconducting flux quantum φ 0. This relationship provides an insight into the effect of the net-current circulating in the annular region and also leads to a precise control to trap or eliminate vortices in flat rings.
Scientific journal, English - Flux-flow instability in 2H-NbSe2 superconducting thin crystals stamped on SiO2/Si substrates
J. Yoshida; H. Ando; N. Kokubo
Journal of Physics: Conference Series, Institute of Physics Publishing, 969, 1, 012073-1-012073-6, 19 Apr. 2018, Peer-reviwed, We have investigated the nonlinear flux flow in the mixed state of 2H-NbSe2 superconducting thin crystals stamped on SiO2/Si substrates. The nonlinearity in the flux flow behavior is marked with upward bending and subsequent voltage jump in the current-voltage characteristics. The results were analyzed within the framework of a modified Larkin-Ovchinnikov model, including the estimation of inelastic relaxation time of quasiparticles in the crystal and heat transfer coefficient between the crystal and SiO2/Si substrate. The analysis provides an insight into the quality of acoustic match at the crystal-substrate interface.
International conference proceedings, English - Direct observation of magnetic flux and interstitial vortices in perforated mesoscopic squares of superconducting films
M Mitsuishi; N Kokubo; K Kitano; S Okayasu; T Nojima; T Sasaki
J. Phys.: Conf. Ser., 969, 012074-1-012074-6, 2018, Peer-reviwed
International conference proceedings, English - Vortex states near absolute zero in a weak-pinning amorphous Mo x Ge1−x film probed by pulsed mode-locking resonance
N. Sohara; A. Ochi; E. Murakami; K. Ienaga; S. Kaneko; N. Kokubo; S. Okuma
Journal of Physics: Conf. Series, 871, 12022, Jul. 2017, Peer-reviwed
Scientific journal, English - Dynamic melting of anisotropy vortex lattice: Velocity dependence
Inoue T.; Ochi A.; Kawamura Y.; Ienaga K.; Kaneko S.; Kokubo N.; Okuma S.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 72.1, 1625-1625, 2017, 傾斜磁場下では傾斜方向に引き伸ばされた2種類の異方的渦糸格子AとBが形成される。Aは1辺が傾斜方向に平行、Bは垂直である。これらを駆動させた状態で、渦糸密度増大による動的融解を調べている。これまでに融解は、A、B共に短辺が等方的格子の融解時の辺にほぼ一致するときに起こること、ピン止めの効かない高速域では、渦糸密度増大により、格子BからAへの変化を経由して完全な液体相へ転移することがわかった。講演ではピン止め効果の効く低速域の結果も示し、異方的格子の動的融解条件を包括的に議論する。
Japanese - Vortex shells in mesoscopic triangles of amorphous superconducting thin films
N. Kokubo; H. Miyahara; S. Okayasu; T. Nojima
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 530, 42-45, Nov. 2016, Peer-reviwed, Direct observation of vortex states confined in mesoscopic regular triangle dots of amorphous Mo-Ge thin films was made with a scanning superconducting quantum interference device microscope. The observed magnetic images illustrate clearly how vortices are distributed over the triangle dots by forming not only commensurate triangular clusters, but also unique patterns imposed by incommensurability. We discuss the results in terms of vortex shells and construct the packing sequence of vortices in the multiple shell structure. (C) 2016 Elsevier B.V. All rights reserved.
Scientific journal, English - Equilibrium and Dynamic Vortex States near Absolute Zero in a Weak Pinning Amorphous Film
Aguri Ochi; Naoya Sohara; Shin-ichi Kaneko; Nobuhito Kokubo; Satoshi Okuma
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 85, 4, 044701-1-044701-7, Apr. 2016, Peer-reviwed, By developing and employing a mode-locking measurement with pulsed currents, we successfully determine the dynamic melting field B-c,dyn(infinity)(T) for a driven vortex lattice of an amorphous MoxGe1-x film in the limit of zero temperature (T -> 0) and complete a dynamic as well as a static vortex phase diagram. At T = 0, the mixed state in the absence of pinning comprises vortex-lattice and quantum-vortex-liquid (QVL) phases, and the melting field separating the two phases is identified as B-c,dyn(infinity)(0). Comparison of the dynamic and static phase diagrams reveals that, when the weak pinning is introduced into the pin-free system, a disordered phase emerges just above the vortex-lattice phase and a threshold field separating the two phases is slightly suppressed from B-c,dyn(infinity)(0), indicative of defect-induced disordering of the lattice. By contrast, a melting field into QVL is much enhanced from B-c,dyn(infinity)(0) up to a point near the upper critical field, resulting in a significant suppression of the QVL phase. This is attributed to the stronger effective pinning at lower T, which survives quantum fluctuations.
Scientific journal, English - Dynamic Melting of Driven Abrikosov Lattices in an Amorphous MoxGe1-x Film in Tilted Field
Aguri Ochi; Yasuki Kawamura; Toshiki Inoue; Tetsuya Kaji; Dobroka Mihaly; Shin-ichi Kaneko; Nobuhito Kokubo; Satoshi Okuma
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 85, 3, 034712-1-034712-6, Mar. 2016, Peer-reviwed, We report a comparative study of the dynamic melting of driven vortex lattices in magnetic field tilted (by theta = 36 degrees) from the normal to the film surface and that of a driven Abrikosov lattice in untilted field (theta = 0). From the mode-locking (ML) resonance, we confirm that vortex lattices in tilted field are stretched in the tilt direction and that, with increasing dc velocity at ML, the shape and orientation of the driven lattice change. Associated with this structural change, the dynamic melting field at which the driven lattice melts also changes. Our results show that, regardless of the lattice shape and orientation, dynamic melting occurs as the shorter side of the distorted lattices reaches close to the side at which the isotropic lattice melts dynamically.
Scientific journal, English - 21pAR-2 Vortex shells in mesoscopic triangles of amorphous superconducting thin films
Kokubo N.; Miyahara H.; Okayasu S.; Nojima T.; Sasaki T.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 71, 1732-1732, 2016
Japanese - Dynamic Melting of Anisotropy Vortex Lattice III
Inoue Toshiki; Ochi A.; Kawamura Y.; Ienaga K.; Kaneko S.; Kokubo N.; Okuma S.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 71, 1439-1439, 2016,これまでの研究により、傾斜磁場下のアモルファスMoxGe1-x膜において異方的渦糸格子が観測された。このとき格子は傾斜方向に引き伸ばされる。我々は渦糸格子を傾斜と垂直方向に高速駆動した時、融解磁場近傍で格子の形状が変化することを明らかにした。本研究ではさらに、渦糸格子を傾斜方向に低速駆動した際にも同様に、融解磁場近傍で格子形状の変化が見られたことを報告する。
Japanese - Observation of vortex states in small superconductors with artificial pinning centres.
Kitano K.; Okayasu S.; Nojima T.; Sasaki T.; Kokubo N.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan, 71, 1505-1505, 2016,ピン止め(小穴)を人工的に導入することにより微小超伝導体の量子渦状態を能動的に制御し、走査SQUID磁気顕微鏡で直接可視化している。今回、正方形状の微小超伝導体に設けたアンチドットの大きさや配置が量子渦配列に与える影響を報告する。
Japanese - Unusual current-voltage characteristics and dynamic correlation of rotating vortex-lattice rings
Y. Kawamura; Y. Matsumura; Y. Yamazaki; S. Kaneko; N. Kokubo; S. Okuma
SUPERCONDUCTOR SCIENCE & TECHNOLOGY, IOP PUBLISHING LTD, 28, 4, 045002-1-045002-7, Apr. 2015, Peer-reviwed, We report the unusual dc current-voltage (I-V) characteristics for the vortex-lattice rings rotated by a dc current I superimposed with ac currents of different amplitudes I-rf in a Corbino disk of an amorphous MoxGe1-x film. As Irf is increased from zero, the I-V curve in the large I region shows a trend to decrease. This is in contrast to the usual behavior of vortex flow in which ac-induced depinning leads to an increase in the flow voltage. We attribute the finding to the I-rf-induced growth in the transverse dynamic correlation of the rotating lattice rings.
Scientific journal, English - Commensurate and Incommensurate Vortex States Confined in Mesoscopic Triangles of Weak Pinning Superconducting Thin Films
Nobuhito Kokubo; Hajime Miyahara; Satoru Okayasu; Tsutomu Nojima
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 84, 4, 043704-1-043704-04, Apr. 2015, Peer-reviwed, We report on the direct observation of vortex states confined in equilateral and isosceles triangular dots of weak pinning amorphous superconducting thin films with a scanning superconducting quantum interference device microscope. The observed images illustrate not only pieces of a triangular vortex lattice as commensurate vortex states, but also incommensurate vortex states including metastable ones. We comparatively analyze vortex configurations found in different sample geometries and discuss the symmetry and stability of commensurate and incommensurate vortex configurations against deformations of the sample shape.
Scientific journal, English - 19aPS-131 Manipulation of vortex states confined in small antidotes in superconducting double layer
Mochizuki R.; Okayasu S.; Nojima T.; Sasaki T.; Kokubo N.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1480-1480, 2015
Japanese - 24aPS-15 Observation of vortex states in mesoscopic triangles of amorphous MoGe superconducting films
Miyahara H.; Okayasu S.; Nojima T.; Kokubo N.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1768-1768, 2015
Japanese - 24aPS-13 Orientation of a vortex lattice driven through nanochannels in superconducting nitride double layers
Yamazaki F.; Mochiduki R.; Kokubo N.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1766-1766, 2015
Japanese - 24aPS-11 Observation of fast driven vortex-lattice flow and effects of anisotropy
Sohara N.; Ochi A.; Kaneko S.; Kokubo N.; Okuma S.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1765-1765, 2015
Japanese - 21pCT-7 Observation of vortex dynamics by pulse mode locking at low temperature II
Ochi A.; Sohara N.; Murakami E.; Kokubo N.; Okuma S.
Meeting Abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 70, 1658-1658, 2015
Japanese - Direct Imaging of Vortex Polygons and Vortex Shells in Mesoscopic Squares of a Weak Pinning Superconducting Thin Film
Nobuhito Kokubo; Satoru Okayasu; Tsutomu Nojima; Hirotaka Tamochi; Bunju Shinozaki
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 83, 8, 083704-1-083704-05, Aug. 2014, Peer-reviwed, We report on the direct visualization of vortices in mesoscopic squares of a weak pinning amorphous superconducting thin film using a scanning superconducting quantum interference device microscope. From systematic measurements made on selected dots, we trace how the vortex pattern evolves with an applied magnetic field. The observed images clearly illustrate the formation of symmetric polygons and concentric shells of vortices, from which the rule of shell filling with increasing vorticity is formulated. We analyze the size and shape of vortex polygons and obtain insight into the flow pattern of the shielding current governing vortex configurations.
Scientific journal, English - Flow and Tilt-Induced Orientation of the Moving Vortex Lattice in Amorphous NbGe Superconducting Thin Films
Nobuhito Kokubo; Tetsuya Yoshimura; Bunjyu Shinozaki
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 82, 9, 094702-1-094702-07, Sep. 2013, Peer-reviwed, The orientation and deformation of moving vortex lattices in the flux-flow state have been investigated in amorphous superconducting NbGe thin films. Employing a mode-locking technique, we detect how moving lattices deform and their orientation changes as a magnetic field is tilted from normal to the film surface. For high tilt angles the lattice orientation is aligned parallely with the tilt direction. Meanwhile for low tilt angles the lattice orientation depends on the vortex velocity and a velocity-induced reorientation occurs. The characteristic velocity for the reorientation varies remarkably as the moving lattices deform. The observed features are consistent with an extended bond-fluctuation theory, revealing that the anisotropic shaking vortex motion is essential for determining the orientation of moving vortex lattices.
Scientific journal, English - Velocity-induced reorientation of a fast driven Abrikosov lattice
S. Okuma; D. Shimamoto; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 85, 6, Feb. 2012, Peer-reviwed, From mode-locking measurements where the vortex lattice is driven quickly by superimposed dc and ac currents, we find a velocity-induced rotation of lattice orientation from a perpendicular to a parallel orientation. This is a dynamic transition caused by increased velocity. At the threshold of the rotation, a characteristic time tau for the vortex to travel one lattice spacing a(0), corresponding to a maximum t for realizing the parallel orientation, turns out to be tau(th) approximate to 10 ns, nearly independent of a(0).
Scientific journal, English - Characteristics of T-c and rho(T) of polycrystalline (In2O3)-(ZnO) films with low carrier density
B. Shinozaki; S. Takada; N. Kokubo; K. Makise; T. Asano; K. Yamada; K. Yano; H. Nakamura
26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, IOP PUBLISHING LTD, 400, 2012, Peer-reviwed, For the polycrystalline (In2O3)-(ZnO) prepared by annealing in air, we investigated the relation among superconductivity, rho(T) characteristics and preparation conditions. To clarify the distribution of elements, we studied the microstructure by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). It was found that 1) The films annealed at restricted regions of annealing temperature T-a and time t(a) show the superconductivity. Transition temperature T-c and carrier density n are T-c<3.3K and n approximate to 10(25)/m(3)similar to 10(26)/m(3), respectively. 2) The data on EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase distribute discretely on grain boundaries and near the interface between the film and the glass substrate. 3) Although data in the T-c -T-a relation are scattered, the T-c shows relatively good correlation with n, taking a convex form.
International conference proceedings, English - Depression of positive magneto-conductance due to anti-weak localization effect in annealed In2O3-ZnO thick films
B. Shinozaki; S. Ezaki; K. Hidaka; K. Makise; T. Asano; N. Kokubo; K. Yamada; K. Yano; H. Nakamura
26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, IOP PUBLISHING LTD, 400, 2012, Peer-reviwed, We investigated the magneto-conductivity Delta - in three dimensional indium zinc oxide films with different resistivity rho prepared by postannealing in air. The weak localization theory was fitted to data of Delta H) at temperatures below 50K by the use of suitable inelastic scattering time tau (T) and spin-orbit(S-O) scattering time tau. We found the rho dependences of both times tau and tau in a range 1.5x10(-3)Omega < rho 300K) < 4 x 10(-6)Omega. As rho increases, the ratio tau/tau increases from approximate to 0.005 to 1.5 and Delta at low temperatures changes from positive to negative values. We suggest a picture that the annealing in air brings the change of the S-O scattering from light to heavy atoms, namely, oxygen to indium and/or zinc atoms.
International conference proceedings, English - Dynamic ordering and lattice orientation of driven vortex matter
S. Okuma; D. Shimamoto; N. Kokubo
26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, IOP PUBLISHING LTD, 400, 022093, 2012, Peer-reviwed, We report on the dynamic ordering and lattice orientation of fast driven vortex matter for an amorphous MoxGe1-x film based on the measurements of the mode-locking resonance. With increasing the velocity, a rotation of the lattice orientation from a perpendicular to parallel orientation takes place, indicative of a dynamic transition. In the middle of the transition region the lattice orientation is neither parallel nor perpendicular, where a characteristic time for the vortex to travel one lattice spacing is tau(th) approximate to 9 ns, which is close to the value obtained at smaller dc velocity. We suggest that tau(th) reflects a quasiparticle recombination time.
International conference proceedings, English - Orientation of a Moving Vortex Lattice in an Amorphous Mo1-xGex Superconducting Film
N. Kokubo; H. Tamochi; B. Shinozaki; T. Nishizaki; N. Kobayashi
26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, IOP PUBLISHING LTD, 400, 022057, 2012, Peer-reviwed, The orientation of a vortex lattice in the flux-flow state of an amorphous Mo1-xGex superconducting film is studied by mode-lock experiments. The formation of a hexagonal moving lattice is observed for a wide range of vortex velocity up to similar to 20 m/s, which is about 1/10 of the critical velocity (similar to 200 m/s) at which the flux-flow instability occurs. The orientation of the hexagonal lattice is observed to be either parallel or perpendicular to the flow direction, and a reorientation occurs at a characteristic velocity (similar to 1 m/s), separating the perpendicular orientation for low velocity from the parallel orientation for high velocity.
International conference proceedings, English - Superconducting characteristics and microstructure of polycrystalline Zn-doped In2O3 films
B. Shinozaki; S. Takada; N. Kokubo; K. Makise; K. Mitsuishi; K. Yamada; K. Yano; H. Nakamura
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 471, 21-22, 717-720, Nov. 2011, Peer-reviwed, In order to investigate the relation among the superconducting transition T., carrier density n, resistivity rho and the microstructure in the polycrystalline (In2O3)(1-x)-(ZnO)(x) films, we prepared specimen films by post annealing of amorphous films with x = 0.025 at various annealing temperature T-a and for annealing time t(a) = 1 h and 4 h. As for microstructures, we have investigated the distribution of elements by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). We have found followings: (1) The annealed films clearly show the superconductivity of which T-c depends on T-a, t(a) and n. This indicates that the superconductivity is determined by the combination of crystallinity and carrier density. (2) The data on STEM-EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase exist inside a film, where the distribution of these droplets dispersed. Therefore, it seems that droplets do not form an electrical conducting path, that is, it is possible that observed superconductivity is due to intrinsic characteristic of polycrystalline (In2O3)(1-x)-(ZnO)(x) films. (C) 2011 Elsevier B.V. All rights reserved.
Scientific journal, English - Quantum melting and lattice orientation of driven vortex matter
S. Okuma; H. Imaizumi; D. Shimamoto; N. Kokubo
Physical Review B - Condensed Matter and Materials Physics, 83, 6, 11 Feb. 2011, Peer-reviwed, We investigate the lattice orientation of driven vortex matter prior to dynamic melting at the field Bc,dyn (i.e., melting for driven vortex lattices) in an amorphous MoxGe1-x film using a mode-locking technique. Under increasing field B at fixed temperatures T, we observe a switching of the lattice orientation from a perpendicular to parallel orientation at a T-dependent characteristic field Bori(T). The shape of the Bori(T) line in the B-T plane resembles that of the dynamic melting line Bc,dyn(T), Bori(T)0.8Bc,dyn(T), while Bc,dyn(T) at low T is significantly suppressed compared to a static melting line due to quantum effects. The results reveal that the lattice rotation occurs as a precursor of dynamic melting instead of static melting and it possibly arises from reduced effective pinning prior to dynamic melting. © 2011 American Physical Society.
Scientific journal, English - Quantum melting and lattice orientation of driven vortex matter
S. Okuma; H. Imaizumi; D. Shimamoto; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 83, 6, 064520-1-064520-7, Feb. 2011, Peer-reviwed, We investigate the lattice orientation of driven vortex matter prior to dynamic melting at the field B-c,B-dyn (i.e., melting for driven vortex lattices) in an amorphous MoxGe1-x film using a mode-locking technique. Under increasing field B at fixed temperatures T, we observe a switching of the lattice orientation from a perpendicular to parallel orientation at a T-dependent characteristic field B-ori(T). The shape of the B-ori(T) line in the B-T plane resembles that of the dynamic melting line B-c,B-dyn(T), B-ori(T) approximate to 0.8B(c,dyn)(T), while B-c,B-dyn(T) at low T is significantly suppressed compared to a static melting line due to quantum effects. The results reveal that the lattice rotation occurs as a precursor of dynamic melting instead of static melting and it possibly arises from reduced effective pinning prior to dynamic melting.
Scientific journal, English - Lattice orientation of driven vortex matter in amorphous superconducting films
D. Shimamoto; S. Okuma; N. Kokubo
INTERNATIONAL SYMPOSIUM: NANOSCIENCE AND QUANTUM PHYSICS 2011 (NANOPHYS'11), IOP PUBLISHING LTD, 302, 012027-1-012027-4, 2011, Peer-reviwed, We present measurements of the mode-locking resonance in the high-field region prior to the dynamic melting field, where driven vortex lattices melt into a moving liquid, in an amorphous MoxGe1-x film. Under increasing field, a switching of the lattice orientation from a perpendicular to parallel orientation is observed at the characteristic field B-ori. We find a trend for the perpendicular orientation to change to the parallel orientation with increasing the lattice velocity in fields just prior to B-ori, while B-ori is not sensitive to the velocity within the range studied. We suggest that the dynamic pinning force moving vortices feel is important for the lattice orientation and is significantly reduced around B-ori as a precursor of dynamic melting.
International conference proceedings, English - Rotating vortex-lattice rings in superconductors
Y. Matsumura; S. Okuma; N. Kokubo
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, ELSEVIER SCIENCE BV, 43, 3, 707-710, Jan. 2011, Peer-reviwed, We report on dynamics of superconducting vortices driven by a radial current in a Corbino disk, where the vortices rotate around the center of the sample by feeling a frustrated Lorentz force inversely proportional to the radius. Based on a mode-locking resonance, we have revealed the formation of rotating vortex rings composed of triangular-lattice arrays. Both at high (4.1 K) and low (2.1 K) temperatures, we have observed the change in the lattice orientation with respect to the flow direction under decreasing field. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English - Novel vortex dynamics in Corbino-disk superconductors
S. Okuma; Y. Yamazaki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 470, S776-S778, Dec. 2010, Peer-reviwed, We study dynamic responses of vortex matter confined and driven in Corbino-disk (CD) superconductors. Under a radial current I. the vortices rotate around the center of CD by feeling a frustrated Lorentz force inversely proportional to the radius of rotation. We find novel vortex dynamics both in zero and nonzero fields B. When I is increased in the vortex-lattice phase, the vortices near the center are first depinned, indicative of the plastic-flow-like rotation, which gradually approaches a laminar flow at large I. We observe a mode-locking resonance, which indicates the formation of rotating vortex rings composed of triangular-lattice arrays. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English - 24aXB-4 Vortex Distributions and Pinning Effect in Mesoscopic superconductors observed by Scanning SQUID Microscopy
Kokubo,N; Okayasu,S; Kanda,A; Shinozaki,B
Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 65, 2, 746, Aug. 2010
Scientific journal, Japanese - Scanning SQUID microscope study of vortex polygons and shells in weak-pinning disks of an amorphous superconducting film
Nobuhito Kokubo; Satoru Okayasu; Akinobu Kanda; Bunju Shinozaki
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 82, 1, 014501-1- 014501-8, Jul. 2010, Peer-reviwed, Direct observation of vortices by the scanning superconducting quantum interference device microscopy was made on large mesoscopic disks of an amorphous MoGe thin film. Owing to the weak pinning nature of the amorphous film, vortices are able to form geometry induced, (quasi-)symmetric configurations of polygons, and concentric shells in the large disks. Systematic measurements made on selected disks allow us to trace not only how the vortex pattern evolves with magnetic field, but also how the vortex polygons change in size and rotate with respect to the disk center. The results are in good agreement with theoretical considerations for mesoscopic disks with sufficiently large diameter. A series of vortex images obtained in a disk with a pinning site reveals a unique line symmetry in vortex configurations, resulting in modifications of the shell filling rule and the magic number.
Scientific journal, English - Transport properties and microstructures of polycrystalline In2O3-ZnO thin films
K. Makise; K. Mitsuishi; N. Kokubo; T. Yamaguchi; B. Shinozaki; K. Yano; K. Inoue; H. Nakamura
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 108, 2, 023704-1-023704-6, Jul. 2010, Peer-reviwed, We prepared polycrystalline In2O3-ZnO films by post annealing the amorphous films (1.0 wt % ZnO) at 200 degrees C with various annealing times t(a) 0 <= t(a) <= 20 h. We have measured the electric resistivity and Hall mobility and also observed film structures by not only the x-ray diffraction but also scanning transmission electron microscopy (STEM) with electron energy-loss spectroscopy (EELS). We have found the following: (1) Hall mobility takes the maximum with respect to the carrier density and the annealed films clearly show the superconductivity of which transition temperature increases with increase in t(a). (2) The data on EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase exist on grain boundaries and near the interface between the film and the glass substrate. However, it seems that these droplets do not form an electrical conducting path but contribute to the scattering centers for carrier electrons, from the dispersed distribution of these droplets in STEM-EELS spectra mapping and the relationship between the electron mean free path and the grain size. (C) 2010 American Institute of Physics. [doi : 10.1063/1.3452375]
Scientific journal, English - Lattice orientations of driven vortex matter in amorphous MoGe films
N. Kokubo; T. Nishizaki; B. Shinozaki; P. H. Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 470, 1, 43-47, Jan. 2010, Peer-reviwed, We have investigated the lattice orientation of driven vortex matter in amorphous MoGe films. Mode locking experiments in the flux flow state reveal that in addition to the theoretically predicted lattice orientation parallel to the flow direction also the perpendicular orientation occurs. Mapping out the orientations in a phase diagram, the perpendicular orientation is found to dominate the phase diagram covering a wide field and temperature range. Scanning tunneling microscopy images of the vortex lattice frozen from the flux flow state confirm the switching between parallel and perpendicular orientations in the phase diagram. The effect is possibly caused by the influence of the sample edge. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English - Dynamic response and ordering of rotating vortices in superconducting Corbino disks
S. Okuma; Y. Yamazaki; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 80, 22, 220501-1-220501-4, Dec. 2009, Peer-reviwed, We study the dynamic response of weakly disordered vortex lattice driven by a radial current I in amorphous superconducting films with a Corbino geometry, where vortices rotate around the center of the sample by a frustrated Lorentz force inversely proportional to the radius. With increasing I, the vortices near the center are first depinned, indicative of the plastic-flow-like rotation, which gradually approaches a laminarlike flow at large I. We observe a mode-locking resonance, which suggests the formation of rotating vortex rings composed of triangular-lattice arrays. The field evolution of the resonance shows the presence of the lattice rotation of the driven vortex rings with respect to the flow direction.
Scientific journal, English - Intrinsic quantum melting of a driven vortex lattice in amorphous Mox Ge1-x films
S. Okuma; H. Imaizumi; N. Kokubo
Physical Review B - Condensed Matter and Materials Physics, 80, 13, 22 Oct. 2009, Peer-reviwed, We observe melting of a driven vortex lattice in amorphous Mox Ge1-x films down to near-zero temperature using a mode-locking technique. We determine the dynamic melting line B c,dyn (T) in nearly the whole field-temperature (B-T) phase diagram. At low T, B c,dyn (T) shows a weak T dependence and is significantly suppressed compared to the mean-field line Bc2 (T) or the static "melting" (depinning) line. The results indicate that intrinsic quantum melting of the vortex lattice decoupled from the underlying pinning potential occurs well below Bc2 at T→0. © 2009 The American Physical Society.
Scientific journal, English - Intrinsic quantum melting of a driven vortex lattice in amorphous MoxGe1-x films
S. Okuma; H. Imaizumi; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 80, 13, 132503-1- 132503-4, Oct. 2009, Peer-reviwed, We observe melting of a driven vortex lattice in amorphous MoxGe1-x films down to near-zero temperature using a mode-locking technique. We determine the dynamic melting line B-c,dyn(infinity)(T) in nearly the whole field-temperature (B-T) phase diagram. At low T, B-c,dyn(infinity)(T) shows a weak T dependence and is significantly suppressed compared to the mean-field line B-c2(T) or the static "melting" (depinning) line. The results indicate that intrinsic quantum melting of the vortex lattice decoupled from the underlying pinning potential occurs well below B-c2 at T -> 0.
Scientific journal, English - Mode locking features of driven vortex matter in an amorphous MoGe film detected by rf impedance technique
N. Kokubo; B. Shinozaki
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 469, 15-20, 1099-1101, Aug. 2009, Peer-reviwed, We have investigated mode locking resonance of a driven vortex lattice in an amorphous MoGe film by means of rf impedance measurements. This technique allows us to detect directly the lattice motion in response to a rf current superimposed on top of a dc current. At low rf currents the resonance appears as jumps (dips) in real (imaginary) part of rf impedance Z. On increasing rf current, the jump height in the real part of Z at a given resonant condition decreases monotonically, whereas the imaginary part of Z exhibits a transformation from the dip to peak behaviors. Namely, the resonant feature changes from capacitive to inductive responses, on increasing rf current. This behavior implies variations in the phase of rf current relative to that of the lattice velocity modulated by the pinning potential. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English - Dynamic melting of driven vortex matter below 1 K
S. Okuma; H. Imaizumi; Y. Suzuki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 469, 15-20, 1063-1066, Aug. 2009, Peer-reviwed, We report on measurements of a mode-locking resonance in amorphous MoxGe1-x films at different temperatures T down to 0.8 K, which is well below the superconducting transition (6 K). We observe dynamic ordering of driven vortex matter for all the temperatures studied. As the field exceeds a certain critical field B-c,B-dyn at fixed T, moving vortices do not exhibit dynamic ordering. At high T, this field B-c,B-dyn(T)so-called dynamic melting, nearly coincides with a characteristic field B-c(T) where the linear resistivity vanishes. At low T, however, B-c,B-dyn(T) is significantly suppressed compared to B-c(T), suggesting intrinsic quantum melting in the absence of pinning. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English - Order-disorder transition and flow noise in an a-MoxGe1-x film
S. Okuma; Y. Suzuki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 469, 15-20, 1096-1098, Aug. 2009, Peer-reviwed, We measure voltage noise spectra S-v(f) generated by current-driven vortices as a function of field B for an amorphous MoxGe1-x film with Corbino-disk geometry. For high voltage V in the flux-flow state, S-v at low frequency (f = 100 Hz) exhibits a sharp peak just below a peak field B-p of the critical (depinning) current. For low V in the plastic-flow state, an additional broad peak of S-v appears at low B in addition to the sharp peak at around B-p. Origin of large noise just below B-p is due to metastable vortex states associated with the order-disorder transition, while that in low B is attributed to pinning-induced incoherent vortex flow. (C) 2009 Published by Elsevier B.V.
Scientific journal, English - Annealing effect on the superconductivity of In2O3-ZnO thin films
B. Shinozaki; N. Kokubo; K. Makise; S. Takada; T. Yamaguti; S. Ogura; K. Yamada; K. Yano; K. Terai; S. Tomai; H. Nakamura
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 469, 15-20, 956-969, Aug. 2009, Peer-reviwed, We have investigated the relation among rho-T characteristics, superconductivity, annealing conditions and the crystallinity of polycrystalline (In2O3)(1-x)-(ZnO)(x) films. We annealed as-grown amorphous films in air by changing annealing temperature and time. It is found that the films annealed at 200 degrees C or 300 degrees C for a time over 0.5 h shows the superconductivity. Transition temperature T-c and the carrier density n are T-c < 3.3 K and n approximate to 10(25)-10(26) m(-3), respectively. Investigations for films with x = 0.01 annealed at 200 degrees C have revealed that the T-c, n and crystallinity depend systematically on annealing time. Further, we consider that there is a suitable annealing time for sharp resistive transition because the transition width becomes wider with longer annealing times. We Studied the upper critical magnetic field H-c2(T) for the film with different annealing time. From the slope of dH(c2)/dT for all films, we have obtained the resistivity p dependence of the coherence length xi(0) at T = 0 K (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English - Broadband Noise of Driven Vortices at the Mode-Locking Resonance
S. Okuma; J. Inoue; N. Kokubo
NOISE AND FLUCTUATIONS, AMER INST PHYSICS, 1129, 117-+, 2009, Peer-reviwed, Vortex-flow noise across the mode-locking (ML) resonance has been studied in an amorphous MoxGe1-x film. We have found that broadband noise (BBN) is remarkably suppressed, when the driven vortex system undergoes ML (dynamic ordering), where current-voltage characteristics show the step-like behavior. The result is consistent with the view of ML freezing that the mode-locked state is a frozen solid pinned in the moving frame of reference. By changing the amplitude of the ac drive, we find the correlation between the sharpness of the ML resonance and suppression of BBN at the ML step.
International conference proceedings, English - Flow Noise of Driven Vortex Matter in Amorphous Superconducting Films
S. Okuma; Y. Suzuki; N. Kokubo
NOISE AND FLUCTUATIONS, AMER INST PHYSICS, 1129, 93-+, 2009, Peer-reviwed, Voltage noise S-V(f) generated by current-driven vortices is studied as a function of flow voltage V and magnetic field for a superconducting amorphous MoxGe1-x film. For high V (or velocity) in the flux-flow state, S-V at low frequency (f=100 Hz) exhibits a sharp peak just below a peak field of the critical current. For low V in the plastic-flow state, an additional broad peak of S-V appears at lower field. Possible origin responsible for large flow noise is discussed. We show that for moderate V, S-V clearly detects the structural phase transition of vortex matter.
International conference proceedings, English - The Hall effect measurements in the high resistance In2O3-ZnO polycrystalline films
K. Yamada; T. Yamaguti; N. Kokubo; B. Shinozaki; K. Yano; H. Nakamura
Transactions of Materials Research Society of Japan, 34, 755-757, 2009, Peer-reviwed
International conference proceedings, English - History dependent vortex configurations in superconducting disks of amorphous MoGe
N. Kokubo; S. Okayasu; A. Kanda; B. Shinzaki
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2, IOP PUBLISHING LTD, 150, 022044-1-022044-4, 2009, Peer-reviwed, We have investigated spatial configurations of vortices in superconducting disks of amorphous MoGe as a function of field history. Employing a scanning SQUID microscope technique, we observe quasi-symmetric distributions of the vortices imposed by the disk geometry. For a field cool measurement, a single vortex state appears after the Meissner state and it is followed by multi-vortex states at higher fields. In a zero field cool (ZFC) measurement, however, different behaviors are observed. On increasing magnetic field, the Meissner state switches directly to the multi-vortex state without showing the single vortex state. The corresponding magnetization curves of the disks are strikingly history dependent. These results indicate that the ZFC procedure results in an unusual penetration of the vortices in the small superconducting disks.
International conference proceedings, English - Field dependent orientation of driven vortex lattice in amorphous MoGe films
N. Kokubo; B. Shinzaki; P. H. Kes
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5, IOP PUBLISHING LTD, 150, 052116-1-052116-4, 2009, Peer-reviwed, We have investigated orientations of a driven vortex lattice in amorphous MoGe films by means of mode locking (ML) techniques. The ML resonance is sensitive to the periodic, vortex spacing along the flow direction and this may allow us to determine the orientations of the driven vortex lattice. We find that the resonant voltage V-ML exhibits a jump like, rapid increase around the peak field H-p of the critical current, on top of a smooth increase with field H as V-ML infinity root H. This result can be interpreted as a lattice rotation between parallel and perpendicular orientations occurring around H-p.
International conference proceedings, English - Order-disorder transition and flow noise for vortices in amorphous films
S. Okuma; Y. Suzuki; K. Kashiro; N. Kokubo
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5, IOP PUBLISHING LTD, 150, 052199-1-052199-4, 2009, Peer-reviwed, In order to examine the universality of edge contamination (EC) and an order-disorder transition (ODT) for vortex matter reported in NbSe2 single crystals, we measure voltage noise spectra S-V (f) induced by current-driven vortices for amorphous MoxGe1-x films with Corbino-disk and striplike geometries. Field dependences of the critical current I c and S-V (f) are nearly independent of contact geometries, indicating that the EC effects are not important on static or dynamic vortex properties in our films. This result is in contrast to what has been reported in NbSe2 crystals. The difference may be attributed to different sample thickness. At 4.1 K, S-V at low frequency f exhibits a sharp peak just below the peak field B p of I-c, suggesting the existence of ODT and metastable vortex states at around B p. At 5.5 K near the superconducting transition T-c(=6.2 K), however, clear evidence for ODT is not visible.
International conference proceedings, English - Dynamic melting of driven vortices at low temperature in a-MoxGe1-x films
S. Okuma; H. Imaizumi; K. Suzuki; Y. Suzuki; N. Kokubo
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5, IOP PUBLISHING LTD, 150, 052200-1-052200-4, 2009, Peer-reviwed, Using a mode-locking technique, we have detected dynamic ordering of driven vortex matter in amorphous MoxGe1-x films at different temperatures T down to 0.8 K, which is well below the superconducting transition (6 K). As the field exceeds a certain critical field B-c,B-dyn at fixed T, moving vortices no longer exhibit dynamic ordering. At high T, this dynamic-melting field B-c,B-dyn (T) nearly coincides with a characteristic field B-c(T) where the linear resistivity vanishes while at low T, B-c,B-dyn(T) is significantly suppressed compared to B-c(T).
International conference proceedings, English - Superconductivity in transparent zinc-doped In2O3 films having low carrier density
K. Makise; N. Kokubo; S. Takada; T. Yamaguti; S. Ogura; K. Yamada; B.Shinozaki; K. Yano; K. Inoue; H. Nakamura
Sci. Technol. Adv. Mater., 9, 044208-1-044208-6, 2009, Peer-reviwed
International conference proceedings, English - Superconductivity in In2O3-ZnO crystalline films
B. Shinozaki; N. Kokubo; S. Takada; T. Yamaguti; K. Yamada; K. Makise; K. Yano; K. Inoue; H. Nakamura
25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PT 5A, IOP PUBLISHING LTD, 150, 5a, 052237-1-052237-4, 2009, Peer-reviwed, Thin In2O3-ZnO (IZO) films were prepared by DC-magnetron sputtering with changing the weight concentration x of ZnO, 0 <= x <= 0.07. As-grown amorphous IZO films show the metallic characteristic but do not show superconductivity. We have investigated the T and H dependence of the resistivity rho and Hall coefficient for annealed films with thickness d = 350 nm in air. It is found that the films with 0 <= x <= 0.03 show superconductivity. Transition temperature T-c and the carrier density n of these films are approximate to 2.0 K and 10(25) - 10(26) m(-3), respectively. The annealed In2O3-ZnO films were examined by a high resolution transparent electron microscopy. This investigation reveals that films annealed at 300 degrees C are sufficient crystalline. There is a difference of crystal structures between the superconducting film and normal film. We studied the upper critical magnetic field H-c2 (T) for the film with x = 0.005. From the slope of dH(c2)/dT, we obtain the coherent length xi(0) approximate to 100 angstrom at T = 0 K and the coefficient of the electronic heat capacity gamma approximate to 3.2 (J/m(3)K(2)) which is small compared with that of other oxide materials.
International conference proceedings, English - 量子化磁束のフロー状態とメゾスコピック性
小久保伸人
九州大学低温センターだより(ISSN 1881-9036), 九州大学低温センター, 3, 3, 22-29, 2009, Peer-reviwed, 超伝導体のピン止め特性の違いを利用して、サブミクロン幅のフロー線路（チャネル）を人工的に作成し、僅か数列にスライスされた磁束格子のフロー特性を調べてきた。磁束運動の周期性を捉えるモードロック共鳴法により、磁束格子が一列ずつ階段状に成長するメゾスコピック性や、チャネル幅と磁束密度のマッチング条件によって変化する磁束秩序構造、さらにこれが磁束ピン止めカの強弱と密接に関連することを明らかにしたので紹介する。
International conference proceedings, Japanese - Shell structures of vortices in superconducting disks of an amorphous MoGe film
N. Kokubo; S. Okayasu; B. Shinozaki
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 468, 15-20, 1316-1318, Sep. 2008, Peer-reviwed, We have investigated spatial configurations of vortices in superconducting disks of an amorphous MoGe film. A scanning SQUID microscope allows us to image vortices magnetically in the disks. Results on the disks with 56 mu m in diameter demonstrate that quasi-symmetric distributions imposed by the circle geometry appear for vorticity up to five. Meanwhile, for vorticity more than six, vortices form shell structures, in which one vortex (two vortices) is located in the center and the others form a ring around. (C) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English - Vortex states in the peak effect regime of a-MoxGe1-x films probed by noise
S. Okuma; K. Kashiro; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 468, 15-20, 1319-1321, Sep. 2008, Peer-reviwed, We present measurements of voltage noise spectra generated by current driven vortices taken at different fields B including the peak-effect regime for a thick a-MoxGe1-x film with Corbino-disk and strip-like contact geometries. The field dependences of the critical current, I-c(B), for both contact geometries are nearly identical to each other, indicating that the edge effects are not important. For the strip-like geometry voltage noise (at low frequency) takes large values around the peak field B-p of I-c(B) and a spectral shape changes drastically just above B-p suggesting that some structural transformation of vortex solid may take place around B-p. (C) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English - Dynamic response of circulating flux flow in amorphous superconducting films
S. Okuma; Y. Suzuki; Y. Yamazaki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 468, 15-20, 1322-1324, Sep. 2008, Peer-reviwed, We report on the dynamic response of the (weakly disordered) vortex lattice to an applied radial current I in the Corbino disk (CD) of amorphous MoxGe1-x films with different diameters (d = 4.6 and 1.6 mm). In CD, the vortices circulate around the center of the sample by feeling a nonuniform Lorentz force inversely proportional to the radius of rotation. We find irrespective of d that, with increasing I in the solid phase, the vortices near the center are first depinned, indicative of the plastic flow-like rotation instead of the elastic rotation. We also find that, with further increasing I, the plastic flow gives way to the liquid-like rotation. In the length range studied the sample size (d) does not affect the dynamic response of vortices. (C) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English - Order-disorder transition of vortex matter in a-Mo(x)Ge(1-x) films probed by noise
S. Okuma; K. Kashiro; Y. Suzuki; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 77, 21, 212505-1-212505-4, Jun. 2008, Peer-reviwed, We measure voltage noise spectra S(V)(f) generated by current-driven vortices at various fields B including the peak-effect regime for amorphous Mo(x)Ge(1-x) films with Corbino-disk and striplike contact geometries. Field dependences of the critical current I(c) and S(V)(f) are nearly independent of contact geometries, indicating that edge effects are not important on static or dynamic vortex properties. This is in contrast to the result reported for NbSe(2) crystals with much larger thickness. S(V)(f) at low frequency f exhibits a sharp peak just below the peak field B(p) of I(c), where the characteristic time of vortex motion increases significantly. The results suggest the existence of the order-disorder transition and vortex instabilities due to coexisting vortex phases at around B(p).
Scientific journal, English - Mode locking and lattice orientations of driven vortex matter in amorphous MoGe films
N. Kokubo; B. Shinozaki; P. H. Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 468, 7-10, 581-584, Apr. 2008, Peer-reviwed, We have investigated flow properties of a current driven, vortex lattice in amorphous MoGe films by mode locking (ML) experiment. ML is a dynamic resonance between a collective velocity modulation of "lattice mode" and a superimposed ac (rf) current on top of a dc current. Tracing the resonance features against magnetic field, we find two specific orientations of lattice flow with respect to the flow direction in the flux-flow state: one is an orientation characterized by a principal axis of the driven lattice parallel to the flow direction, and the other is another orientation where one of the lattice axes is perpendicular to the flow direction. (c) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English - Motion of current-driven vortex solids with weak pinning in the Corbino disk
S. Okuma; Y. Suzuki; Y. Yamazaki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 468, 7-10, 613-616, Apr. 2008, Peer-reviwed, We report on the dynamic response of a weakly disordered vortex lattice driven by a radial current I in an amorphous MoxGe1-x film with a Corbino-disk (CD) geometry. In CD, the vortices circulate around the center of the sample by feeling a nonuniform Lorentz force inversely proportional to the radius of rotation. We observe the peak in the dynamic critical current, as well as, in the static critical current, as a function of the magnetic field. This means that, even when the vortices are in circular motion, they feel the maximum pinning force just prior to 'dynamic' melting. As I is increased in the solid state, the vortices near the center are first depinned and then exhibit the plastic-flow-like rotation. This is in contrast to previous work for a YBa2Cu3O7-delta single-crystal, in which the elastic rotation is observed. (c) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English - Observation of an extended magnetic field penetration in amorphous superconducting MoGe films
Taichiro Nishio; Satoru Okayasu; Jun-ichi Suzuki; Nobuhito Kokubo; Kazuo Kadowaki
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 77, 5, 052503-1-052503-4, Feb. 2008, Peer-reviwed, We have observed the magnetic field distribution of a vortex generated in amorphous (alpha)-MoGe thin films with various thicknesses (d) (<lambda, where lambda is the penetration depth) with a scanning superconducting quantum interference device microscope. From the analyses of the field distribution as functions of film thickness and temperature, it is found that an effective in-plane penetration depth (Lambda) extends with decreasing d, in accordance with the Pearl prediction Lambda=2 lambda(2)/d. Temperature dependence of Lambda is also consistent with the two-fluid model involving the Pearl prediction.
Scientific journal, English - Suppression of broadband noise at mode locking in driven vortex matter
S. Okuma; J. Inoue; N. Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 76, 17, 172503-1-172503-4, Nov. 2007, Peer-reviwed, We measure voltage noise generated by current-driven vortices for fields corresponding to the solid phase when at equilibrium including the peak-effect regime, focusing on a change in broadband noise (BBN) as the vortex system undergoes a mode-locking (ML) resonance. For all the fields steplike structure indicative of ML is observed in the I-V curves. We find that BBN at high frequencies (but well below the ac drive frequency) is suppressed inside the ML steps. The results are consistent with the view that the mode-locked state is a frozen solid pinned in the moving frame of reference.
Scientific journal, English - Peak anomaly of dynamic critical current in NbSe2 crystals
N. Kokubo; T. Asada; K. Kadowaki; K. Takita
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 463, 229-231, Oct. 2007, Peer-reviwed, We present flow dynamics of vortex matter in the peak effect regime of 2H-NbSe2 crystals investigated by mode locking (ML) and dc transport measurements. Dynamic critical current, characterizing dynamic friction of driven vortices, exhibits a peak behavior against magnetic field and this anomaly occurs above the peak field of the critical current. In fields between these peak behaviors, the NIL resonance, characterizing the lattice flow in driven vortices, disappears. The vanishing field of the ML resonance increases with frequency and saturates at high frequency. This saturation behavior will be discussed within a dynamic ordering model and also be compared to the peak anomaly of the dynamic critical current. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - Vortex phase diagram and dynamics at low temperature in a thick a-MoxGe1-x film
S. Okuma; K. Suzuki; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 463, 232-235, Oct. 2007, Peer-reviwed, We study the vortex phase diagram and dynamics in the low-temperature liquid phase of a thick amorphous a-MoxGe1-x film with weak pinning. The vortex solid state is ordered vortex lattice or Bragg glass, which is different from the disordered vortex glass of a-MoxSi1-x films with stronger pinning. We find, however, that the vortex liquid state is similar to that for the a-MoxSi1-x films, involving the quantum-vortex-liquid phase at low temperature, where we again detect the unusual vortex flow. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - Mode locking and noise of driven vortices near the peak-effect regime
S. Okuma; J. Inoue; N. Kokubo
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 463, 290-293, Oct. 2007, Peer-reviwed, We present the measurements of broadband voltage noise generated by the driven vortices near the peak-effect regime of a thick amorphous MoxGe1-x film. We focus on a change in voltage noise as the vortex system undergoes mode locking (ML), which is a dynamic resonance between the ac drive superimposed on the dc drive and lattice-oscillation modes excited collectively. By sweeping the dc current I at fixed ac drive, we find the step-like structure in the current-voltage (I-V) characteristics indicative of M L. At high frequencies f (but well below the ac-drive frequency) the noise spectrum is f-independent. We find a trend for the amplitude of noise (at high f) to decrease in the ML step. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - A trial usage of microprobes for improvement of a scanning SQUID microscope
S. Okayasu; N. Kokubo; I. Kakeya
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 463, 294-296, Oct. 2007, Peer-reviwed, A scanning SQUID microscope is a powerful tool for direct observations of vortices. Magnetic sensitivity is high enough, but spatial resolution is limited by the size of pickup coils. To improve the spatial resolution, a trial usage of microprobe on the pickup coil was achieved. Obtained images are expanded about four times, and the attached microprobe acts as a magnetic lens. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - Broadband noise across the mode-locking freezing in driven vortex matter
S. Okuma; J. Inoue; N. Kokubo
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, WORLD SCIENTIFIC PUBL CO PTE LTD, 21, 18-19, 3379-3386, Jul. 2007, Peer-reviwed, We report on the measurements of broadband voltage noise generated by the driven vortex matter in and just below the peak-effect regime of a thick amorphous MoxGe1-x film. We focus on a change in broadband noise as the system undergoes the mode-locking (ML) resonance (ML freezing), which occurs when the ac drive superimposed on the de drive excites the lattice-oscillation modes collectively. Independent of the field studied, the noise spectrum at low frequencies f is of Lorentzian type, while it is f-independent at high f (but well below the ac-drive frequency). We find that the magnitude of noise at high f decreases in the ML resonance.
Scientific journal, English - Vortex states and peak effect at low temperature in thick amorphous films with weak pinning
S. Okuma; K. Kashiro; N. Kokubo
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, WORLD SCIENTIFIC PUBL CO PTE LTD, 21, 18-19, 3387-3393, Jul. 2007, Peer-reviwed, We report on the dynamic as well as static properties of vortices in the low-temperature (T) solid phase of a thick amorphous MoxGe1-x film with weak pinning. The vortex-solid state is considered to be a weakly disordered vortex lattice, which is inferred from the mode-locking resonance over the broad field region. The peak effect of the critical current 1, with magnetic field is clearly visible down to the lowest T measured (0.2 K), which corresponds to 3.3 % of the superconducting transition temperature. We find that largest voltage noise originating from current-driven vortices appears in the field region just prior to the peak field at which I, takes a peak. This is in accord with the result reported in NbSe2 single crystals.
Scientific journal, English - Dynamic ordering of driven vortex matter in the peak effect regime of amorphous MoGe films and 2H-NbSe2 crystals
N. Kokubo; T. Asada; K. Kadowaki; K. Takita; T. G. Sorop; P. H. Kes
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 75, 18, 184512-1-184512-8, May 2007, Peer-reviwed, Dynamic ordering of driven vortex matter has been investigated in the peak effect regime of both amorphous MoGe films and 2H-NbSe2 crystals by mode locking (ML) and dc transport measurements. ML features allow us to trace how the shear rigidity of driven vortices evolves with the average velocity. Determining the onset of ML resonance in different magnetic fields and/or temperatures, we find that the dynamic ordering frequency (velocity) exhibits a striking divergence in the higher part of the peak effect regime. Interestingly, this phenomenon is accompanied by a pronounced peak of dynamic critical current. Mapping out field-temperature phase diagrams, we find that divergent points follow well the thermodynamic melting curve of the ideal vortex lattice over wide field and/or temperature ranges. These findings provide a link between the dynamic and static melting phenomena which can be distinguished from the disorder induced peak effect.
Scientific journal, English - Vortex phase diagram and dynamics near T=0 probed by voltage noise in amorphous superconducting films
S. Okuma; K. Suzuki; N. Kokubo
NOISE AND FLUCTUATIONS, AMER INST PHYSICS, 922, 237-+, 2007, Peer-reviwed, We report on the equilibrium vortex phase diagram and vortex dynamics driven by do current at low temperature in a thick amorphous (a-)MoxGe1-x film with weak pinning. The vortex solid state is a weakly disordered vortex lattice, which is different from the disordered vortex glass for the a-MoxSi1-x films with stronger pinning. For both systems the liquid state is similar to each other, involving the quantum-vortex-liquid (QVL) phase at low temperature, where we detect large vortex-flow noise. The unusual flow persists even in the solid phase just below the QVL phase, while its amplitude is remarkably suppressed.
International conference proceedings, English - Vortex states near the peak effect regime detected by voltage noise
S. Okuma; K. Kashiro; N. Kokubo
Noise and Fluctuations, AMER INST PHYSICS, 922, 245-248, 2007, Peer-reviwed, We study the static and dynamic properties of vortices in the vortex solid phase of a thick amorphous MoxGe1-x film with Corbino-disk (CD) and strip-like contact geometries. For the strip-like geometry the peak effect (PE) of the critical currently with magnetic field is clearly visible for all the temperatures studied and large voltage noise originating from current-driven vortices appears in the field region just prior to a peak field where 1, takes a peak. For the CD geometry we observe essentially the same phenomena, indicating that the edge effects are not important for the static or dynamic properties of vortices.
International conference proceedings, English - Noise and mode-locking resonance of driven vortices in Type-II superconductors
S. Okuma; J. Inoue; N. Kokubo
NOISE AND FLUCTUATIONS, AMER INST PHYSICS, 922, 233-+, 2007, Peer-reviwed, Voltage noise generated by the driven vortices in and just below the peak-effect regime of a thick amorphous MoxGe(1-x) film is presented, focusing on a change in broadband noise as the system undergoes the mode-locking (ML) resonance. ML occurs when the ac drive superimposed on the do drive excites the lattice-oscillation modes collectively. Except for the field near the melting field, the noise spectrum is frequency (f)-independent at high f. We find that for all the fields studied the magnitude of noise at high f decreases in the ML resonance.
International conference proceedings, English - Mode locking of vortex matter in the peak effect regime of amorphous MoGe films
N. Kokubo; K. Kadowaki; P. H. Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 445, 206-209, Oct. 2006, Peer-reviwed, We have investigated flow properties of vortex matter in the peak effect regime of amorphous MoGe films by a mode locking (ML) technique. While dc current-voltage (I-V) characteristic exhibits a S-shaped anomaly, we observed striking frequency dependence in a ML feature: above a minimum frequency to observe the ML resonance, the maximized ML width increases with frequency and seems to saturate at high frequency. A comparison indicates that the I-V anomaly does not coincide with the onset of ML, but occurs in. a velocity range where fractions of mode locked vortices increase rapidly with velocity. (c) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English - Vortex-slip transitions in superconducting a-NbGe mesoscopic channels
N Kokubo; TG Sorop; R Besseling; PH Kes
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 73, 22, 224514 -1-224514 -8, Jun. 2006, Peer-reviwed, Intriguing and novel physical aspects related to the vortex flow dynamics have been recently observed in mesoscopic channel devices of a-NbGe with NbN channel edges. In this work we have systematically studied the flow properties of vortices confined in such mesoscopic channels as a function of the magnetic field history, using dc-transport and mode-locking (ML) measurements. As opposed to the field-down situation, in the field-up case a kink anomaly in the dc I-V curves is detected. The mode-locking measurements reveal that this anomaly is, in fact, a flow induced vortex slip transition: by increasing the external drive (either dc or ac) a sudden change occurs from n to n+2 moving vortex rows in the channel. The observed features can be explained in terms of an interplay between field focusing due to screening currents and a change in the predominant pinning mechanism.
Scientific journal, English - Dynamical melting and mode locking of vortex matter in 2H-NbSe2 pure single crystals
N Kokubo; K Kadowaki; K Takita
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 437-38, 149-152, May 2006, Peer-reviwed, We have investigated flow properties of vortex matter around the peak effect region in 2H-NbSe2 pure single crystals by mode locking (ML) techniques. ML is a dynamic synchronization phenomenon between ac drive superimposed on dc drive and collective lattice modes excited over the driven vortex lattice. Around the peak effect regime, we observe the vanishing of the ML resonance, which is velocity dependent: At small velocity, ML vanishes just below the peak field H, for the peak effect, while at large velocity, it vanishes above H, The velocity dependence of the vanishing field agrees qualitatively with a dynamical melting picture proposed by Koshelev and Vinokur. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - History dependent vortex flow dynamics in mesoscopic channels
TG Sorop; N Kokubo; R Besseling; PH Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 437-38, 285-288, May 2006, Peer-reviwed, Intriguing and novel physical aspects related to the vortex flow dynamics have been recently observed in mesoscopic channel devices of a-NbGe with NbN channel edges. In this work we have studied the flow properties of such confined vortices as a function of the magnetic field history, using dc-transport and mode-locking (ML) measurements. As opposed to the field down situation, in field up case a kink anomaly in the dc I-V curves is detected. The mode-locking measurements unveil the dynamic change in the flow configurations around this anomaly: n moving rows of vortex array at low velocity changes suddenly to n + 2 rows at high velocity around the anomaly. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - 27aXF-5 MODE LOCKING AND DYNAMICAL ORDER OF VORTEX MATTER
Kokubo,N; Kadowaki,K; Takita,K
Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 61, 1, 769, Mar. 2006
Scientific journal, Japanese - 27aXF-6 Dynamic Critical Current and Dynamic Melting of Vortex Matter
Asada,T; Kokubo,N; Kadowaki,K; Takita,K
Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 61, 1, 769, Mar. 2006
Scientific journal, Japanese - Dynamic ordering of vortex matter in amorphous MoGe films
N. Kokubo; S. Okayasu; K. Kadowaki
LOW TEMPERATURE PHYSICS, PTS A AND B, AMER INST PHYSICS, 850, 853-+, 2006, Peer-reviwed, We report flow properties of vortex matter near the peak effect regime of amorphous MoGe films detected by mode locking (ML) experiment. The ML features allow us to define clearly the dynamic ordering transition separating incoherent flow state at low velocity from a coherent flow state at high velocity. On raising temperature the ordering velocity increases and seems to show a diverging behavior in the higher part of the peak effect regime.
International conference proceedings, English - Mode locking of vortex matter in NbSe2 pure single crystals
N. Kokubo; K. Kadowaki; K. Takita
LOW TEMPERATURE PHYSICS, PTS A AND B, AMER INST PHYSICS, 850, 843-+, 2006, Peer-reviwed, We present the mode locking (ML) phenomenon of vortex matter observed in a layered superconductor of 2H-NbSe2 pure single crystal. On application of ac current on top of dc current, clear ML resonance appears in differential conductance voltage curves, indicating the presence of elastic modes excited collectively over driven vortices. On increasing magnetic field, the ML voltage shows square root dependence on field, consistent with the ML condition for vortex matter.
International conference proceedings, English - Peak effect and dynamic melting of vortex matter in NbSe2 crystals
N Kokubo; K Kadowaki; K Takita
PHYSICAL REVIEW LETTERS, AMER PHYSICAL SOC, 95, 17, 177005-1-177005-4, Oct. 2005, Peer-reviwed, We present a mode locking (ML) phenomenon of vortex matter observed around the peak effect regime of 2H-NbSe2 pure single crystals. The ML features allow us not only to trace how the shear rigidity of driven vortices persists on approaching the second critical field, but also to demonstrate a dynamic melting transition of driven vortices at a given velocity. We observe the velocity dependent melting signatures in the peak effect regime, which reveal a crossover between the disorder-induced transition at small velocity and the thermally induced transition at large velocity. This uncovers the relationship between the peak effect and the thermal melting.
Scientific journal, English - 20aPS-92 Mode locking of vortex matter in BI-2212 single crystals
Asada,T; Kokubo,N; Yamamoto,T; Kadowaki,K
Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 60, 2, 448, Aug. 2005
Scientific journal, Japanese - 25aXL-5 Thickness dependence of the effective penetration depth in a thin film
Nishio,T; Okayasu,S; Suzuki,J; Kokubo,N; Kadowaki,K
Meeting abstracts of the Physical Society of Japan, The Physical Society of Japan (JPS), 60, 1, 737, Mar. 2005
Scientific journal, Japanese - Effect of field history on the confinement of vortices in mesoscopic channels
N Kokubo; R Besseling; PH Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 412, 362-366, Oct. 2004, Peer-reviwed, We investigated vortex flow in mesoscopic channels and its field history dependence using mode locking (ML) experiments. In the channel system the critical current I-c oscillates with magnetic field due to a series of structural transitions from n to n+/-1 confined rows. In presence of a combined rf and dc current, ML is observed in the dc current-voltage curve. The field dependence of the ML voltage directly yields the evolution of n with field. We observed strong differences in the I-c oscillations and the evolution of n for different field history. The data show that matching effects in the channels are governed by the effective channel width which strongly depends on screening current flowing along the channel edges. (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Dynamical fluctuations in mode locking experiments on vortices moving through mesoscopic channels
N Kokubo; R Besseling; PH Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 408, 573-574, Aug. 2004, Peer-reviwed, We have studied flow properties of vortices driven through easy flow mesoscopic channels by means of mode locking (ML) technique. We observe ML jump with large voltage broadening in a real part of rf impedance. Upon approaching the pure dc flow by reducing rf amplitude, the NIL jump is smeared out by the divergence of the voltage width. This indicates a large spread of internal frequency of driven channel vortices and lack of coherence in dc state. (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Vortex matter driven through mesoscopic channels
PH Kes; N Kokubo; R Besseling
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 408, 478-481, Aug. 2004, Peer-reviwed, The dynamics of vortex matter confined to mesoscopic channels has been investigated by means of mode locking experiments. When vortices are coherently driven through the potential provided by static vortices pinned in the channel edges, interference between the washboard frequency of the moving vortex lattice and the frequency of the superimposed rf-drive causes (Shapiro-like) steps in the dc-I-V curves. The position of the voltage steps uniquely determines the number of moving rows in each channel. It also shows how the frustration between row spacing and channel width behaves as a function of magnetic field. Maxima in flow stress (similar toI(c)) occur at mismatch conditions. They are related to the traffic-jam-like flow impedance caused by the disorder in the edges. At higher fields, near the 2D-melting line B-m(T), the mode-locking interference characteristic for crystalline motion, strongly depends on the velocity, i.e. the applied frequency at which the vortex motion is probed. The minimum velocity at which coherent motion could be observed, diverges when the melting line is approached from below. Above the melting line interference is absent for any frequency. These observations give the first direct evidence for a dynamic phase transition of vortex matter driven through a disorder potential as predicted by Koshelev and Vinokur. (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Vortex lattice dynamics in a-NbGe detected by mode-locking experiments
R Besseling; O Benningshof; N Kokubo; PH Kes
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 408, 581-582, Aug. 2004, Peer-reviwed, We observed mode-locking (ML) of rf-dc driven vortex arrays in a superconducting weak pinning a-NbGe film. The ML voltage shows the expected scaling V proportional to f rootB with f the rf-frequency and B the magnetic field. For large de-velocity (corresponding to a large ML frequency), the NIL current step width exhibits a squared Bessel function dependence on the rf-amplitude as predicted for NIL of a lattice moving elastically through a random potential. (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments
N Kokubo; R Besseling; PH Kes
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 69, 6, 064504-1-064504-10, Feb. 2004, Peer-reviwed, The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow us to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of three rows we obtain (i) the pinning frequency f(p), (ii) the onset frequency f(c) for ML (proportional to ordering velocity), and (iii) the fraction L-ML/L of coherently moving three-row regions in the channel. The field dependence of these quantities shows that, at matching, where L-ML is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where L-ML is small, both the pinning force and the ordering velocity are enhanced. Further, we find that f(c)proportional tof(p)(2), consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.
Scientific journal, English - Magnetic imaging of a two dimensional vortex by scanning SQUID microscopy
T. Nishio; S. Okayasu; J. Suzuki; N. Kokubo; K. Kadowaki
NANOFAB CREST abstracts, 150, 2004, Peer-reviwed
English - Dynamic melting of confined vortex matter
R Besseling; N Kokubo; PH Kes
PHYSICAL REVIEW LETTERS, AMERICAN PHYSICAL SOC, 91, 17, 177002-1-177002-4, Oct. 2003, Peer-reviwed, We study dynamic melting of confined vortex matter moving in disordered, mesoscopic channels by mode-locking experiments. The dynamic melting transition, characterized by a collapse of the mode-locking effect, strongly depends on the frequency, i.e., on the average velocity of the vortices. The associated dynamic ordering velocity diverges upon approaching the equilibrium melting line T-m,T-e(B) as v(c)similar to(T-m,T-e-T)(-1). The data provide the first direct evidence for velocity dependent melting and show that the phenomenon also takes place in a system under disordered confinement.
Scientific journal, English - Mode-locking and dynamic melting of vortex matter driven through mesoscopic channels
R Besseling; N Kokubo; PH Kes
JOURNAL DE PHYSIQUE IV, E D P SCIENCES, 12, PR9, 169-171, Nov. 2002, Peer-reviwed, We investigated the dynamics of vortex matter confined to mesoscopic channels by means of mode locking experiments. When vortices move coherently through the pinning (shear) potential provided by static vortices in the channel edges, interference between the washboard frequency of the lattice and the frequency of superimposed rf-currents causes (Shapiro-like) steps in the dc-IV curves. These steps allow to trace directly how the number of moving rows in each channel and the frustration between row spacing and channel width, varies with magnetic field. The flow stress (similar to I-c) surprisingly exhibits maxima for mismatching (defective) structures, originating from traffic-jam-like flow due to disorder in the edges. We then focus on the behavior for higher fields, approaching the 2D melting field B-m. In this regime the presence of the interference phenomenon, characteristic for crystalline motion, strongly depends on the velocity (applied frequency) at which vortices are probed. The minimum velocity to observe coherent, solid-like motion is found to diverge when the field is increased towards B-m, above which the interference is absent for any frequency. This provides the first direct evidence for a velocity dependent, dynamic phase transition of vortex matter moving through disorder, as predicted by Koshelev and Vinokur.
Scientific journal, English - Mode locking of vortex matter driven through mesoscopic channels
N Kokubo; R Besseling; VM Vinokur; PH Kes
PHYSICAL REVIEW LETTERS, AMERICAN PHYSICAL SOC, 88, 24, 247004-1-247004-4, Jun. 2002, Peer-reviwed, We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the IV curves provide detailed information on how both the number of vortex rows and the lattice structure in each flow channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when the incoherent motion of mixed n and n +/- 1 row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasistatic fault zones with misoriented edge dislocations induced by disorder in the channel edges.
Scientific journal, English - Current-induced voltage noise at zero field in thick and thin films of a-MoxSi1-x
S Okuma; M Kamada; N Kokubo
PHYSICA C, ELSEVIER SCIENCE BV, 357, 560-563, Aug. 2001, Peer-reviwed, We have performed current-voltage (I-V) and current-induced voltage noise S-V measurements of thick (100 nm) and thin (6 nm) films of amorphous MoxSi1-x to study vortex dynamics in zero field (B = 0) below the transition temperature T-c. It is commonly observed that (i) the large 1/f-type noise appears in the low current region where the I-V characteristics show strong nonlinearity; (ii) with increasing I at fixed T, S-V/V (at low frequency f) decreases; and (iii) by applying small B or with increasing T, S-V/V decreases drastically. These results are consistent with the view that large noise at B = 0 is due to density fluctuations of thermally excited and subsequently grown vortex loops and dissociated vortex-antivortex pairs for thick and thin films, respectively. At high I the spectral shape of the thick film. differs from that of the thin film. For the thick film the presence of the long characteristic time has been suggested. (C) 2001 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Hall-conductivity sign change and fluctuations in amorphous NbxGe1-x films
N. Kokubo; J. Aarts; P. H. Kes
Physical Review B, 64, 014507-1-014507-5, Jun. 2001, Peer-reviwed
Scientific journal, English - Vortex phase diagram of disordered films of granular In and amorphous MoxSi1-x
S Okuma; M Arai; N Kokubo
PHYSICA B, ELSEVIER SCIENCE BV, 284, 640-641, Jul. 2000, Peer-reviwed, The vortex states in the disordered films of granular In and amorphous MoxSi1-x have been studied. For a thick In film convincing evidence for the vortex-glass transition (VGT) has been obtained from both DC and AC resistivities in a certain field range, while for a thick MoxSi1-x film critical behavior for the VGT has been observed only in DC measurements. This suggests that the strength and/or structure of pinning centers may play an important role in the critical behavior of the VGT. We will also show that the phase diagram is drastically altered for a thin him. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Vortex dynamics in the mixed state of amorphous MoxSi1-x films
N Kokubo; S Okuma
PHYSICA B, ELSEVIER SCIENCE BV, 284, 865-866, Jul. 2000, Peer-reviwed, We have performed the current-voltage and voltage-noise measurements for uniformly disordered thick amorphous MoxSi1-x films in various fields B. Below the melting field B-m where the depinning current I-C drops rapidly, the 1/f broad-band noise (BBN) is observed for I > I-C. Compared with the recent simulation results, we find that the BBN originates from the plastic flow motion of vortices. We have also observed the large lif BBN at and near zero field, where its origin is different from the plastic flow motion. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Current-induced voltage noise below the Kosterlitz-Thouless transition
N Kokubo; M Mutou; M Kamada; S Okuma
PHYSICA B, ELSEVIER SCIENCE BV, 284, 981-982, Jul. 2000, Peer-reviwed, We have measured the current-voltage (I-V) characteristics and voltage-noise spectral density S-V(f) for very thin amorphous MoxSi1-x films far below the Kosterlitz-Thouless transition temperature. The large 1/f-like noise is observed over broad frequencies f in a current range where the I-V curve shows a strong nonlinearity. The noise spectra, S-V(f)/V (divided by V), for different I show a trend to collapse onto a single line of 1/f(beta) (beta approximate to 0.75) at high f: The characteristic frequency f(C) below which S-V(f)/V deviates downward from the 1/f(beta) line increases rapidly with increasing I. The observed noise cannot be explained by the simple shot noise model of vortices. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Vortex dynamics in amorphous MoxSi1-x films detected by voltage noise
S Okuma; N Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 61, 1, 671-677, Jan. 2000, Peer-reviwed, We have measured the current-induced voltage noise SV for both the thick and thin films of amorphous MoxSi1-x with strong pinning, over a broad frequency range, to study the effects of both the current I and magnetic field B on the vortex dynamics. The results show that the vortex dynamics probed by S-V strikingly depends on the static vortex states. Irrespective of the film thickness, noise is largest at B similar to 0, while small vortex shot noise is observed at high B in the vortex-liquid phase. The origin of large noise at B similar to 0 is due mainly to density fluctuations of the thermally excited and subsequently grown vortex loops and dissociated vortex-antivortex pails for three dimensions (3D) and 2D, respectively, in the presence of an applied current. In the three-dimensional vortex-solid phase, the 1/f(beta)(beta<0.6)-like noise spectra resulting from a plastic-flow motion of vortices are observed at low I over the broad field region, which is attributed to high concentration of pinning centers. With increasing I in the nonlinear regime, both the amplitude and spectral exponent beta of S-V decrease and eventually approach the values in the vortex-liquid phase.
Scientific journal, English - Vortex dynamics below the Kosterlitz-Thouless transition detected by voltage noise
S Okuma; N Kokubo; M Kamada
ADVANCES IN SUPERCONDUCTIVITY XII, SPRINGER-VERLAG TOKYO, XII, 1, 296-298, 2000, Peer-reviwed, We have made simultaneous current-voltage (I - V) and voltage noise Sv measurements of thin (6-nm thick) amorphous MoxSi1-x films to study vortex dynamics below the Kosterlitz-Thouless transition temperature in the presence of the current. In the current region where the I - V characteristics show strong nonlinearity, the large 1/f-type noise is observed. At high frequency f the spectrum Sv(f)/V (Sv(f) divided by V) for different I seems to collapse onto a single straight line. Below the characteristic frequency fc, Sv(f)/V deviates downward from the straight line. The characteristic time tau(C) = 1/f(C) is much larger than the travelling time of each free vortex across the sample, implying the presence of the long-time correlation of dissociated vortices.
International conference proceedings, English - The T=0 phase diagram of the field-driven superconductor-insulator transition in 2D
S. Okuma; S. Shinozaki; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), XI, 1, 185-188, 1999, Peer-reviwed
International conference proceedings, English - The vortex-glass transition and phase diagram in low-TC superconductors
S. Okuma; M. Arai; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), XI, 1, 203-206, 1999, Peer-reviwed
International conference proceedings, English - Dynamical properties of vortices in the mixed state of amorphous MoxSi1-x
N. Kokubo; S. Okuma
Advances in Superconductivity (Springer-Verlag, Tokyo), XI, 1, 295-298, 1999, Peer-reviwed
International conference proceedings, English - The thermally nucleated dissipation process in zero field studied by voltage noise
N. Kokubo; M. Muto; S. Okuma
Advances in Superconductivity (Springer-Verlag, Tokyo), XI, 1, 299-302, 1999, Peer-reviwed
International conference proceedings, English - Anomalous magnetoresistance near the superconductor-insulator transition in ultrathin films of alpha-MoxSi1-x
S Okuma; T Terashima; N Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 58, 5, 2816-2819, Aug. 1998, Peer-reviwed, We have made systematic studies for both the zero-field and field-driven superconductor-insulator transitions in a series of 4-nm-thick films of amorphous MoxSi1-x at temperatures T down to similar to 0.05 K and fields B up to 15 T. For superconducting films, we have observed an anomalous peak in the magnetoresistance R(B) and a subsequent decrease in R(B) with increasing B at low temperatures in fields higher than the critical field B-xxC. This result, together with finding that the magnetoresistance is always positive for insulating films, may suggest the presence of localized Cooper pairs even at B>B-xxC in the limit of T-->0.
Scientific journal, English - Voltage noise of an amorphous MoxSi1-x film near the superconducting transition in magnetic fields
N Kokubo; T Terashima; S Okuma
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 67, 3, 725-728, Mar. 1998, Peer-reviwed, The voltage noise S-v(f) in a thick amorphous MoxSi1-x film is studied over a broad frequency range spanning six decades (f = 0.1 Hz-100 kHz) in magnetic fields just above and below the melting field, as a function of a steady current. The origin of the low-frequency (f approximate to 0.1-10 Hz) noise observed near the zero-resistance region is mainly due to temperature fluctuations and the contribution due to flux motion is very small. In contrast, S-v(f) at higher frequencies (f approximate to 10 Hz-100 kHz) appears to be dominated by the flux motion. These results are compared with recent experiments on YBa2Cu3O7-delta films.
Scientific journal, English - Superconductor-insulator transition driven by magnetic-field and disorder in two-dimensional MoxSi1-x films
S. Okuma; T. Terashima; N. Kokubo
Solid State Communications, Elsevier Ltd, 106, 8, 529-533, 1998, Peer-reviwed, We have made systematic measurements for the field-swept superconductor-insulator (S-I) transition over a wide range of disorder through the disorder-driven S-I transition using very thin amorphous MoxSi1-x films with a fixed thickness of 4 nm. Critical resistances determined from both the field-driven and disorder-driven S-I transitions are found to be nonuniversal and apparently smaller than RQ ∼ 6.5 kΩ. © 1998 Elsevier Science Ltd. All rights reserved.
Scientific journal, English - Frequency dependence of the complex resistivity in the vortex state
S. Okuma; T. Ito; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), X, 1, 75-78, 1998, Peer-reviwed
International conference proceedings, English - Voltage noise measurements in dirty superconducting films
N. Kokubo; T. Terashima; S. Okuma
Advances in Superconductivity (Springer-Verlag, Tokyo), X, 1, 79-82, 1998, Peer-reviwed
International conference proceedings, English - Hall effect in the mixed state of In film
S. Okuma; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), X, 1, 93-96, 1998, Peer-reviwed
International conference proceedings, English - Superconductor-insulator transition in two-dimensional a-MoxSi1-x films
S. Okuma; T. Terashima; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), X, 1, 163-166, 1998, Peer-reviwed
International conference proceedings, English - Universal critical scaling of dc and ac complex resistivities in an indium film near the vortex-glass transition
S Okuma; N Kokubo
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 56, 21, 14138-14142, Dec. 1997, Peer-reviwed, We have made ac complex resistivity measurements from 100 Hz to 5 MHz in the linear regime, as well as de resistivity measurements, for a thick indium film in constant magnetic fields B. At B = 0.1 T, the vortex-glass transition temperature T-g can be defined from the frequency-independent phase of the ac resistivity, which is in good accordance with the value determined independently from de measurements. Critical exponents (v similar to 1.4, z similar to 8) extracted from both de and ac measurements are consistent. In addition to the vortex-correlation length xi(g)(T), the vortex-relaxation time tau(g)(T) is directly obtained from the frequency dependence of the ac resistivity. Within a limited critical regime (\T-T-g\ similar to>0.1 K) about the phase transition, the amplitude and phase of the ac resistivity as well as the de resistivity follow the universal scaling functions, which resemble those found in YBa2Cu3O7. In B=1 T, we have observed the similar scaling behavior for the de resistivity to that in B=0.1 T, whereas degradation of the scaled isotherms is visible for the ac resistivity. Although this problem still awaits further studies, all of these findings offer strong experimental evidence for the second-order transition in indium films.
Scientific journal, English - Scaling behavior of the longitudinal and Hall resistivities in indium films
S Okuma; N Kokubo
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 56, 1, 410-415, Jul. 1997, Peer-reviwed, We have made simultaneous measurements of the longitudinal rho(xx) and Hall rho(xy) resistivities for granular films of indium with different thicknesses ((t) over bar = 12, 20, and 60 nm) and the normal-state resistivities (rho(xxn) = 2-5x10(-5) Omega m) at temperatures T down to 0.5 K and in fields B up to 7 T. A striking scaling behavior expressed as rho(xy)(T)=A rho(xx)(T)(beta) has been observed for all the films studied irrespective of (t) over bar and rho(xxn) at fixed fields which are not close to a critical field B-C. In the mixed state (B<B-C and T<T-C, where T-C is the transition temperature), the coefficient A and exponent beta (=2-3) are nearly independent of the field strength B and the film thickness (t) over bar. In the vicinity of the field-driven superconductor-insulator transition, we have found the unusual insulating region B-xxC<B<B-xyC, where B-xxC and B-xyC represent critical fields determined by rho(xx) and rho(xy), respectively, which tends to grow with increasing rho(xxn) and/or decreasing (t) over bar, This region is similar to one found previously by Paalanen, Hebard, and Ruel in amorphous InOx thin films, and the present result is consistent with their notion that the insulating region corresponds to the Bose-glass insulator.
Scientific journal, English - Scaling behavior of the longitudinal and Hall resistivities in indium films
S. Okuma; N. Kokubo
Physical Review B - Condensed Matter and Materials Physics, 56, 1, 410-415, 1997, Peer-reviwed, We have made simultaneous measurements of the longitudinal (Formula presented) and Hall (Formula presented) resistivities for granular films of indium with different thicknesses ((Formula presented) 20, and 60 nm) and the normal-state resistivities (Formula presented) at temperatures (Formula presented) down to 0.5 K and in fields (Formula presented) up to 7 T. A striking scaling behavior expressed as (Formula presented) has been observed for all the films studied irrespective of (Formula presented) and (Formula presented) at fixed fields which are not close to a critical field (Formula presented) In the mixed state ((Formula presented) and (Formula presented) where (Formula presented) is the transition temperature), the coefficient (Formula presented) and exponent β (Formula presented) are nearly independent of the field strength (Formula presented) and the film thickness (Formula presented) In the vicinity of the field-driven superconductor-insulator transition, we have found the unusual insulating region (Formula presented) where (Formula presented) and (Formula presented) represent critical fields determined by (Formula presented) and (Formula presented) respectively, which tends to grow with increasing (Formula presented) and/or decreasing (Formula presented) This region is similar to one found previously by Paalanen, Hebard, and Ruel in amorphous (Formula presented) thin films, and the present result is consistent with their notion that the insulating region corresponds to the Bose-glass insulator. © 1997 The American Physical Society.
Scientific journal, English - Universal critical scaling of dc and ac complex resistivities in an indium film near the vortex-glass transition
S. Okuma; N. Kokubo
Physical Review B - Condensed Matter and Materials Physics, 56, 21, 14138-14142, 1997, Peer-reviwed, We have made ac complex resistivity measurements from 100 Hz to 5 MHz in the linear regime, as well as dc resistivity measurements, for a thick indium film in constant magnetic fields (Formula presented) At (Formula presented) the vortex-glass transition temperature (Formula presented) can be defined from the frequency-independent phase of the ac resistivity, which is in good accordance with the value determined independently from dc measurements. Critical exponents ((Formula presented), (Formula presented)) extracted from both dc and ac measurements are consistent. In addition to the vortex-correlation length (Formula presented) the vortex-relaxation time (Formula presented) is directly obtained from the frequency dependence of the ac resistivity. Within a limited critical regime (Formula presented) about the phase transition, the amplitude and phase of the ac resistivity as well as the dc resistivity follow the universal scaling functions, which resemble those found in (Formula presented) In (Formula presented) we have observed the similar scaling behavior for the dc resistivity to that in (Formula presented) whereas degradation of the scaled isotherms is visible for the ac resistivity. Although this problem still awaits further studies, all of these findings offer strong experimental evidence for the second-order transition in indium films. © 1997 The American Physical Society.
Scientific journal, English - Superconductor-insulator transition in uniformly disordered two-dimensional films
S. Okuma; T. Terashima; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), IX, 1, 191-194, 1997, Peer-reviwed
International conference proceedings, English - Critical scaling behavior in the ac impedance of indium films in magnetic fields
N. Kokubo; S. Okuma
Advances in Superconductivity (Springer-Verlag, Tokyo), IX, 1, 195-198, 1997, Peer-reviwed
International conference proceedings, English - Ac magnetic and mechanical response at the onset of superconductivity in magnetic fields
S. Okuma; H. Yoshida; T. Ito; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), IX, 1, 199-202, 1997, Peer-reviwed
International conference proceedings, English - UNUSUAL INSULATING PHASE AT LOW-TEMPERATURE IN THIN INDIUM FILMS
S OKUMA; N KOKUBO
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 51, 21, 15415-15419, Jun. 1995, Peer-reviwed
Scientific journal, English - FIELD-INDUCED SUPERCONDUCTOR-INSULATOR TRANSITION AND GRAIN-SIZE IN THIN GRANULAR FILMS OF INDIUM
S OKUMA; N KOKUBO
SOLID STATE COMMUNICATIONS, PERGAMON-ELSEVIER SCIENCE LTD, 93, 12, 1019-1023, Mar. 1995, Peer-reviwed, Magnetic field, B, is used to tune two-dimensional granular films of indium with average grain sizes of 14 nm (Film G1), 22 nm (Film G2) and 28 nm (Film G3) through the superconductor-insulator (S-I) transition. Far Film G1 the resistance, R(T,B), near the S-I transition obeys the scaling function which is similar to that observed in the amorphous film of indium with thickness about 3 nm, while for Films G2 and G3 deviations from the scaling behaviors are visible. The results are discussed in terms of a transformation of the system from a dirty superconductor to a Josephson network or inhomogeneities of the parameters in the Josephson network.
Scientific journal, English - Scaling of the Hall resistance in the mixed state of indium films
S. Okuma; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), VII, 1, 113-116, 1995, Peer-reviwed
International conference proceedings, English - Distinct insulating phase at low temperature in thin superconducting films
S. Okuma; N. Kokubo
Advances in Superconductivity (Springer-Verlag, Tokyo), VII, 1, 117-120, 1995, Peer-reviwed
International conference proceedings, Japanese - Thickness dependence of the I-V characteristics in indium films
S. Okuma; K. Enya; H. Hirai; N. Kokubo; T. Arai
Advances in Superconductivity (Springer-Verlag, Tokyo), VII, 1, 121-124, 1995, Peer-reviwed
International conference proceedings, English - Power-law behavior of I-V characteristics and magnetoresistance in thin indium films
S. Okuma; N. Kokubo; K. Enya
Advances in Superconductivity (Springer-Verlag, Tokyo), VI, 1, 119-122, 1994, Peer-reviwed
International conference proceedings, English
MISC
- SQUID on tip made of a superconducting nitride film by a self-aligned deposition method using a reactive DC magnetron sputtering
N. Kokubo; B. Gerelkhuu
Lead, Jan. 2024, 電子通信情報学会超伝導エレクトロニクス研究会, Japanese, Invited, Technical report - 超伝導薄膜リングにおける磁束集束効果と渦糸捕捉
小久保伸人; 三石真里江; 岡安悟; 野島勉; 佐々木孝彦
2019, 日本物理学会講演概要集(CD-ROM), 74, 1, 2189-079X, 201902243569646786 - 走査SQUID顕微鏡で観測した微小超伝導体の渦糸・反渦糸状態
小久保伸人; 岡安悟; 野島勉; 佐々木孝彦
2018, 日本物理学会講演概要集(CD-ROM), 73, 1, 2189-079X, 201802283884815803 - アンチドットをもつ微小正方形アモルファス超伝導膜の磁束状態
北野恒平; 小久保伸人; 三石真里江; 岡安悟; 野島勉; 佐々木孝彦
2017, 日本物理学会講演概要集(CD-ROM), 72, 1, 2189-079X, 201702242555078877 - 微細孔をもつ微小な正方形超伝導体の磁束状態
小久保伸人; 北野恒平; 三石真里江; 岡安悟; 野島勉; 佐々木孝彦
2017, 日本物理学会講演概要集(CD-ROM), 72, 1, 2189-079X, 201702278090777393 - アンチドットをもつ微小アモルファス超伝導体の磁束状態
三石真里江; 小久保伸人; 岡安悟; 野島勉; 佐々木孝彦
2017, 日本物理学会講演概要集(CD-ROM), 72, 2, 2189-079X, 201702283836390444 - 幾何学的な構造を持つ微小超伝導体に閉じ込めた磁束状態
小久保 伸人; 岡安 悟; 野島 勉
東北大学極低温科学センター, Nov. 2015, 東北大学極低温科学センターだより, 16, 8-11, Japanese, 40020905717 - 幾何学的構造を持つ微小超伝導体に閉じ込めた量子渦配列
小久保伸人
アグネ技術センター, Aug. 2015, 固体物理, 594, 8, 437-446, Japanese, Peer-reviwed, Introduction other, 0454-4544, 40020568668, AN00092629 - 8pBB-1 Observation of vortex dynamics by pulse mode locking at low temperature
Ochi A.; Sohara N.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 22 Aug. 2014, Meeting abstracts of the Physical Society of Japan, 69, 2, 565-565, Japanese, 1342-8349, 110009874107, AA11439205 - 8pBB-9 Direct observation of vortices in triangles of amorphous MoGe superconducting films
Miyahara H.; Okayasu S.; Nojima T.; Kokubo N.
The Physical Society of Japan (JPS), 22 Aug. 2014, Meeting abstracts of the Physical Society of Japan, 69, 2, 567-567, Japanese, 1342-8349, 110009874109, AA11439205 - 8pBB-3 Instability of vortex flow by increased velocity and its origin
Sohara N.; Ochi A.; Kaneko S.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 22 Aug. 2014, Meeting abstracts of the Physical Society of Japan, 69, 2, 565-565, Japanese, 1342-8349, 110009875920, AA11439205 - 27pCA-3 Velocity-induced rearrangement and instability of driven vortex lattices
Ochi A.; Nagatani K.; Sohara N.; Kokubo N.; Okuma S
The Physical Society of Japan (JPS), 05 Mar. 2014, Meeting abstracts of the Physical Society of Japan, 69, 1, 790-790, Japanese, 1342-8349, 110009836409, AA11439205 - 27pCA-2 Observation of fast driven vortex-lattice flow by pulse measurements and effects of anisotropy
Sohara N.; Takahashi M.; Nagatani K.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 05 Mar. 2014, Meeting abstracts of the Physical Society of Japan, 69, 1, 790-790, Japanese, 1342-8349, 110009836408, AA11439205 - Instability and Rearrangement of Fast Driven Abrikosov Lattice
Sohara A.; Nagatani K.; Kokubo A.; Okuma S.
The Physical Society of Japan (JPS), 26 Aug. 2013, Meeting abstracts of the Physical Society of Japan, 68, 2, 723-723, Japanese, 1342-8349, 110009755943, AA11439205 - 26pEM-1 Attractive force between vortices in fast driven vortex lattice II
Nagatani K.; Sohara N.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 26 Mar. 2013, Meeting abstracts of the Physical Society of Japan, 68, 1, 860-860, Japanese, 1342-8349, 110009645527, AA11439205 - 18aAF-1 Attractive force between vortices in fast driven vortex lattice
Nagatani K.; Shimamoto D.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 24 Aug. 2012, Meeting abstracts of the Physical Society of Japan, 67, 2, 718-718, Japanese, 1342-8349, 110009601128, AA11439205 - 24aBC-1 速度による渦糸格子方位の回転と微視的機構(24aBC 超伝導,領域6(金属,超低温,超伝導・密度波))
大熊 哲; 嶋本 大祐; 小久保 伸人
一般社団法人日本物理学会, 05 Mar. 2012, 日本物理学会講演概要集, 67, 1, 829-829, Japanese, 1342-8349, 110009567875, AA11439205 - 21aHC-1 Change in lattice orientation of driven vortex solid by flow velocity III
Shimamoto D.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 24 Aug. 2011, Meeting abstracts of the Physical Society of Japan, 66, 2, 796-796, Japanese, 1342-8349, 110008760161, AA11439205 - 25aEH-2 Change in lattice orientation of driven vortex solid by flow velocity II
Shimamoto D.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 03 Mar. 2011, Meeting abstracts of the Physical Society of Japan, 66, 1, 809-809, Japanese, 1342-8349, 110008715171, AA11439205 - 25aEH-3 Vortex states and dimensionality of amorphous Mo_xGe_<1-x> films
Sato H.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 03 Mar. 2011, Meeting abstracts of the Physical Society of Japan, 66, 1, 809-809, Japanese, 1342-8349, 110008715172, AA11439205 - 24aXB-9 Change in microscopic structure of rotated vortex-lattice rings II
Matsumura Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2010, Meeting abstracts of the Physical Society of Japan, 65, 2, 747-747, Japanese, 1342-8349, 110008099274, AA11439205 - 24aXB-8 Change in lattice orientation of driven vortex solid by flow velocity
Shimamoto D.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2010, Meeting abstracts of the Physical Society of Japan, 65, 2, 747-747, Japanese, 1342-8349, 110008099273, AA11439205 - 20aHX-8 Change in microscopic structure of rotated vortex-lattice rings
Matsumura Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 01 Mar. 2010, Meeting abstracts of the Physical Society of Japan, 65, 1, 813-813, Japanese, 1342-8349, 110007656825, AA11439205 - 20aHX-7 Dynamic quantum melting of vortex solid and flow states in vortex lattice II
Okuma S.; Imaizumi H.; Shimamoto D.; Kokubo N.
The Physical Society of Japan (JPS), 01 Mar. 2010, Meeting abstracts of the Physical Society of Japan, 65, 1, 813-813, Japanese, 1342-8349, 110007656824, AA11439205 - 26aYA-9 Rotated rings of vortex lattice III
Matsumura Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2009, Meeting abstracts of the Physical Society of Japan, 64, 2, 697-697, Japanese, 1342-8349, 110007498548, AA11439205 - 26aYA-7 Dynamic quantum melting of vortex solid and flow states of vortex lattice
Imaizumi H.; Matsumura Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2009, Meeting abstracts of the Physical Society of Japan, 64, 2, 697-697, Japanese, 1342-8349, 110007498546, AA11439205 - 28aYJ-1 Dynamic quantum melting of vortex solid III
Imaizumi H.; Matsumura Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 03 Mar. 2009, Meeting abstracts of the Physical Society of Japan, 64, 1, 776-776, Japanese, 1342-8349, 110007372627, AA11439205 - 超伝導渦の動的秩序化
大熊哲; 井上甚; 小久保伸人
アグネ技術センタ-, 2009, 固体物理, 515, 1, 1-15, Japanese, Peer-reviwed, Introduction other, 0454-4544, 40016447968, AN00092629 - 21pYE-4 Order-disorder transition in the vortex solid phase of amorphous Mo_xGe_<1-x> films II
Suzuki Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 25 Aug. 2008, Meeting abstracts of the Physical Society of Japan, 63, 2, 702-702, Japanese, 1342-8349, 110006985101, AA11439205 - 21pYE-7 Rotated rings of vortex lattice II
Yamazaki Y.; Inoue J.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 25 Aug. 2008, Meeting abstracts of the Physical Society of Japan, 63, 2, 703-703, Japanese, 1342-8349, 110006985104, AA11439205 - 24pTH-1 Mode-locking resonance nad broadband noise II
Inoue J.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63, 1, 768-768, Japanese, 1342-8349, 110007194807, AA11439205 - 24pTH-3 Dynamic quantum melting of vortex solid
Okuma S.; Suzuki K.; Suzuki Y.; Imaizumi H.; Inoue J.; Kokubo N.
The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63, 1, 769-769, Japanese, 1342-8349, 110007192119, AA11439205 - 24pTH-2 Order-disorder transition in the vortex solid phase of amorphous Mo_xGe_<1-x> films
Suzuki Y.; Kashiro K.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63, 1, 768-768, Japanese, 1342-8349, 110007192118, AA11439205 - 24pTH-5 Rotated rings of vortex lattice
Yamazaki Y.; Suzuki Y.; Inoue J.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63, 1, 769-769, Japanese, 1342-8349, 110007192120, AA11439205 - 21aXQ-10 Vortex dynamics in the vortex solid phase and influences of edges
Kashiro K.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 21 Aug. 2007, Meeting abstracts of the Physical Society of Japan, 62, 2, 803-803, Japanese, 1342-8349, 110007142100, AA11439205 - 21aXQ-9 Mode-locking resonance and broadband noise
Inoue J.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 21 Aug. 2007, Meeting abstracts of the Physical Society of Japan, 62, 2, 802-802, Japanese, 1342-8349, 110007142101, AA11439205 - 21aXQ-11 Dynamics of rotated vortex solid and size effects
Yamazaki Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 21 Aug. 2007, Meeting abstracts of the Physical Society of Japan, 62, 2, 803-803, Japanese, 1342-8349, 110007142099, AA11439205 - 18aRD-11 Vortex dynamics in the vortex solid phase of amorphous Mo_xGe_<1-x> films
Kashiro K.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 28 Feb. 2007, Meeting abstracts of the Physical Society of Japan, 62, 1, 766-766, Japanese, 1342-8349, 110007192977, AA11439205 - 18aRD-10 Mode locking of vortex flow and voltage noise II
Inoue J.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 28 Feb. 2007, Meeting abstracts of the Physical Society of Japan, 62, 1, 765-765, Japanese, 1342-8349, 110007192978, AA11439205 - 23aZA-14 Peak-effect of amorphous Mo_xGe_<1-x> films at low temperature
Kashiro K.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2006, Meeting abstracts of the Physical Society of Japan, 61, 2, 633-633, Japanese, 1342-8349, 110007179307, AA11439205 - 23aZA-8 Mode locking of vortex flow and voltage noise in amorphous Mo_xGe_<1-x> films
Inoue J.; Katagiri T.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 18 Aug. 2006, Meeting abstracts of the Physical Society of Japan, 61, 2, 631-631, Japanese, 1342-8349, 110007182525, AA11439205 - 26pWA-5 Study of substitution effect on Bi_2Sr_2Ca(Cu_<1-x>M_x)_2(M=Zn,Co,Ni)O_<8+δ> single crystals doped with magnetic and nonmagnetic impurities
Yamamoto T; Kakeya I; Kokubo N; Kadowaki K
The Physical Society of Japan, 2005, Meeting Abstracts of the Physical Society of Japan, 60, 0, 585-585, Japanese, 1342-8349, 110004536344, AA11439205 - 19aYL-5 Observation of the vortex state in Nb thin film embedded ferromagnetic dot by decoration method
Sato H; Yamamoto T; Kokubo N; Kakeya I; Kadowaki K
The Physical Society of Japan, 2005, Meeting Abstracts of the Physical Society of Japan, 60, 0, Japanese, 110004559353 - 19aYL-7 Observation of flux lines on Nb thin films prepared with various geometric patterns
Yamamoto T; Kakeya I; Kokubo N; Kadowaki K
The Physical Society of Japan, 2005, Meeting Abstracts of the Physical Society of Japan, 60, 0, Japanese, 110004559355 - 28aPS-51 Magnetic phase diagram of MgB_2 single crystal synthesized under the ambient pressureII
Yasuda J; Kakeya I; Kokubo N; Kadowaki K
The Physical Society of Japan, 2004, Meeting Abstracts of the Physical Society of Japan, 59, 0, 567-567, Japanese, 1342-8349, 110002193571, AA11439205 - 14aRB-4 Vortex state of Bi_2Sr_2CaCu_2O_<8+δ> doped by magnetic impurities
Yamamoto T.; Kakeya I.; Kokubo N.; Kadowaki K.
The Physical Society of Japan, 2004, Meeting Abstracts of the Physical Society of Japan, 59, 0, 517-517, Japanese, 1342-8349, 110002054232, AA11439205 - 14pRC-3 Magnetic properties of MgB_2 single crystal
Yasuda J.; Kakeya I.; Kokubo N.; Kadowaki K.
The Physical Society of Japan, 2004, Meeting Abstracts of the Physical Society of Japan, 59, 0, 532-532, Japanese, 1342-8349, 110002054333, AA11439205 - 13aPS-17 Study on Josephson Vortex Flow Dynamics in Mesoscopic Intrinsic Junctions
Yamazaki T; Kakeya I; Iwase M; Yamamoto T; Kokubo N; Kadowaki K
The Physical Society of Japan, 2004, Meeting Abstracts of the Physical Society of Japan, 59, 0, Japanese, 110002053831 - Effective penetration depth in thin superconducting films obtained by a SQUID microscope
T. Nishio; S. Okayasu; J. Suzuki; N. Kokubo; K. Kadowaki
2004, FIMS/ITS-NS/CTC/PLASMA 2004 abstracts, II-117, English - Vortex Dynamics in Amorphous Mo_x_Si_1-x_ Films Detected by Voltage Noise
S.Okuma; N.Kokubo
2000, Phys. Rev. B, 61, 1, 671-677, 0163-1829, 80011427199 - 27aYM-9 Vortex Dynamics Observed by Voltage Noise Far below the KT Transition
Kamada M.; Kokubo N.; Okuma T.
The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54, 2, 722-722, Japanese, 1342-8349, 110001994089, AA11439205 - 27aYM-8 Complex ac Impedance Measurements and Vortex States in Disordered Superconductors
Arai M.; Imamoto Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54, 2, 721-721, Japanese, 1342-8349, 110001994088, AA11439205 - 28a-K-7 Vortex States in Disordered Superconductors Detected by AC Magnetic Response
Arai M.; Imamoto Y.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 15 Mar. 1999, Meeting abstracts of the Physical Society of Japan, 54, 1, 528-528, Japanese, 1342-8349, 110002223490, AA11439205 - 29p-A-6 The Effect of Magnetic Field on He adsorption on an amorphous Mo_xSi_<1-x> Film
Aoki H.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 15 Mar. 1999, Meeting abstracts of the Physical Society of Japan, 54, 1, 591-591, Japanese, 1342-8349, 110002224500, AA11439205 - 29p-B-4 Voltage Noise Measurements of Amorphous Mo_xSi_<1-x> films in Magnetic Fields II
Kokubo N.; Muto M.; Kamada M.; Okuma S.
The Physical Society of Japan (JPS), 15 Mar. 1999, Meeting abstracts of the Physical Society of Japan, 54, 1, 594-594, Japanese, 1342-8349, 110002224546, AA11439205 - 29p-B-2 Vortex States and Dimensionality of Amorphous Mo_xSi_<1-x> Films at Very Low Temperatures
Shinozaki S.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 15 Mar. 1999, Meeting abstracts of the Physical Society of Japan, 54, 1, 593-593, Japanese, 1342-8349, 110002224538, AA11439205 - Vortex States and ac Magnetic Response of Amorphous Mo_xSi_<1-x> Films
ARAI M.; KOKUBO N.; OKUMA S.
The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53, 2, 698-698, Japanese, 1342-8349, 110001984117, AA11439205 - Voltage Noise Measurements of Amorphous Mo_xSi_<1-x> Films in Magnetic Fields
KOKUBO N.; MUTOU M.; SHINOZAKI S.; OKUMA S.
The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53, 2, 698-698, Japanese, 1342-8349, 110001984118, AA11439205 - Phase Diagram of the Two-Dimensional Superconductor-Insulator Transition at T=0
SHINOZAKI S.; KOKUBO N.; OKUMA S.
The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53, 2, 684-684, Japanese, 1342-8349, 110001984063, AA11439205 - Voltage Noise Measurements of Superconducting Films in Magnetic Fields II
KOKUBO N.; OKUMA S.
The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53, 1, 585-585, Japanese, 1342-8349, 110002207521, AA11439205 - Anomalous Magnetoresistance near the Superconductor-Insulator Transition
OKUMA S.; TERASHIMA T.; KOKUBO N.
The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53, 1, 586-586, Japanese, 1342-8349, 110002207537, AA11439205 - AC Magnetic Response of Superconducting Films Close to the Vortex-Glass Transition II
ITO T.; ARAI M.; KOKUBO N.; OKUMA S.
The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53, 1, 588-588, Japanese, 1342-8349, 110002207572, AA11439205 - The KT Transition and Voltage Noise in Amorphous Mo_xSi_<1-x> Films
MUTOU M.; KOKUBO N.; SHINOZAKI S.; OKUMA S.
The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53, 1, 588-588, Japanese, 1342-8349, 110002207567, AA11439205 - Anomalous Magnetoresistance near the Superconductor-Insulator Transition in Ultrathin Films of a-Mo┣D2x┫D2Si┣D21-x┫D2
S.Okuma T.Terashima; N.Kokubo
1998, Phys. Rev., 58, 5, 2816-2819, 0163-1829, 80010476345 - 7p-L-4 Wetting Transition of ^4He film on Alkari Metal Surface
Aoki H; Kokubo N; Okuma S
The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52, 2, 664-664, Japanese, 1342-8349, 110002063463, AA11439205 - 5a-K-3 Voltage Noise Measurements of Superconducting Films in Magnetic Fields
Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52, 2, 587-587, Japanese, 1342-8349, 110002062898, AA11439205 - 5a-K-4 AC Magnetic Response of Superconducting Films Close to the Vortex-Glass Transition
ITO T.; KOKUBO N.; OKUMA S.
The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52, 2, 587-587, Japanese, 1342-8349, 110002062900, AA11439205 - 5a-K-8 Superconductor-Insulator Transition in Amorphous Mo_xSi_<1-x> films III
Terashima T.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52, 2, 588-588, Japanese, 1342-8349, 110002062907, AA11439205 - 28p-Q-5 Voltage Noise Measurements of Indium Films in Magnetic Fields
Kokubo N; Okuma S
The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52, 1, 582-582, Japanese, 1342-8349, 110002136734, AA11439205 - 28p-Q-4 Superconductor-Insulator Transition in Amorphous Mo_xSi_<1-x> films II
Terashima T; Kokubo N; Okuma S
The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52, 1, 581-581, Japanese, 1342-8349, 110002136729, AA11439205 - 28p-Q-6 AC Magnetic Response of Indium Films Close to the Vortex-Grass Transition
ITO T; KOKUBO N; OKUMA S
The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52, 1, 582-582, Japanese, 1342-8349, 110002136742, AA11439205 - 極低温下水晶振動子法による膜厚・吸着原子の測定
大熊哲; 小久保伸人
アグネ技術センタ-, 1997, 固体物理, 32, 2, 97-103, Japanese, Peer-reviwed, Introduction other, 0454-4544, 40001389541, AN00092629 - a.c.susceptibility measurement of superconducting films using mutual inductive method
Ito T.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996, 3, 506-506, Japanese, 110001986956, AN10453836 - Superconductor-Insulator Transition in Amorphous Mo_xSi_<1-x> films
Terashima T.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996, 3, 505-505, Japanese, 110001986954, AN10453836 - The Hall Effect in the Mixed State of Indium Films and Amorphous Mo_xSi_<1-x> Films
Okuma S.; Terashima T.; Kokubo N.
The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996, 3, 505-505, Japanese, 110001986953, AN10453836 - AC Impedance Measurements of Indium Films in Magnetic Fields II
Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996, 3, 506-506, Japanese, 110001986955, AN10453836 - 3a-YK-13 AC Impedance Measurements of In Films in Magnetic Fields
Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 15 Mar. 1996, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 51, 3, 515-515, Japanese, 110009790889, AN10451127 - Tunneling Measurements Close to the SI Transition in 2D II
Arai T.; Kokubo N.; Okuma S.
The Physical Society of Japan (JPS), 12 Sep. 1995, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1995, 3, 356-356, Japanese, 110002057018, AN10453836 - Scaling of the Hall Resistance in the Mixed State of the Superconductors
Kokubo N; Okuma S
The Physical Society of Japan (JPS), 16 Mar. 1995, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 50, 3, 397-397, Japanese, 110002227412, AN10451127 - 2次元超伝導体における磁場印加超伝導絶縁体転移
小久保伸人
物性研究刊行会, 1995, 物性研究出版, 64, 3, 282-307, Japanese, Introduction other, 0525-2997, 110006437625, AN0021948X - 3p-YD-2 S-I Transition by Magnetic Field and the Hall Effect
Kokubo N; Arai T; Okuma S
The Physical Society of Japan (JPS), 16 Aug. 1994, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1994, 3, 303-303, Japanese, 110001990120, AN10453836 - 31a-YF-5 S-I Transition by Magnetic Field and the Hall Effect
Kokubo N; Okuma S
The Physical Society of Japan (JPS), 16 Mar. 1994, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 49, 3, 436-436, Japanese, 110002236350, AN10451127 - 13a-D-8 Superconductor-Insulator Transition in Quench-Condensed Indium Films II
Okum S.; Kokubo N.; Enya K.
The Physical Society of Japan (JPS), 20 Sep. 1993, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1993, 3, 392-392, Japanese, 110001997051, AN10453836
Books and other publications
- 超伝導磁束状態の物理
小久保伸人
Textbook, Japanese, Contributor, 3.3.2 幾何学的に閉じ込められた磁束の配列, 裳華房, 05 Apr. 2017, 9784785329228 - The Oxford Handbook of Small Superconductors
Nobuhito Kokubo; Satoru Okayasu; Kazuo Kadowaki
Scholarly book, English, Contributor, Chapter 3: MULTI-VORTEX STATES IN MESOSCOPIC SUPERCONDUCTORS, Oxford University Press, Jan. 2017, 9780198738169
Lectures, oral presentations, etc.
- SQUID on tip made of a superconducting nitride film by a self-aligned deposition method using a reactive DC magnetron sputtering
小久保 伸人
Invited oral presentation, Japanese, 電子情報通信学会超伝導エレクトロニクス研究会, Invited
14 Jan. 2025
14 Jan. 2025- 14 Jan. 2025 - 広い温度範囲で利用できるニオブチタン窒化膜を用いた先端型ナノSQUIDの開発
小久保伸人
Japanese, 第29回渦糸物理ワークショップ
19 Dec. 2023 - 窒化ニオブチタン膜を用いた先端型ナノ SQUID の輸送特性
小久保伸人
Poster presentation, Japanese, 日本物理学会第78回年次大会
18 Sep. 2023 - 針状ガラスの先端を用いたNV中心ダイヤモンド磁気センサの作製
マンカケイ; 小久保伸人
Poster presentation, Japanese, 第70回応用物理学会春季学術講演会
16 Mar. 2023 - ガラス針先端のナノSQUIDを探針とした走査型熱・磁気顕微鏡の開発
磯部陽州; 上原諒; 小久保伸人; 島田宏
Poster presentation, Japanese, 第70回応用物理学会春季学術講演会
16 Mar. 2023 - 針状ガラス管先端を利用した超伝導センサの開発：超伝導熱・磁気顕微鏡を目指して
小久保伸人
Japanese, ナノトライボロジー研究センター第４回 シンポジウム
08 Mar. 2023 - Observation of vortex trapping and expulsion in superconducting rings of amorphous MoGe thin films
N. Kokubo; S. Okayasu; T. Nojima
Poster presentation, English, 32th International Symposium on Superconductivity, Kyoto, Miyako Messe, International conference
03 Dec. 2020 - 微小超伝導体の渦糸トラップとアンチドットクラスタの磁束状態
小久保伸人; 岡安悟; 野島勉
Oral presentation, Japanese, 第27回渦糸物理ワークショップ, ボルテックスフォーラム, 京都大学理学研究科セミナーハウス, Domestic conference
18 Dec. 2019 - Observation of vortex trapping and expulsion in superconducting rings of amorphous MoGe thin films
N. Kokubo; S. Okayasu; T. Nojima
Poster presentation, English, 32th International Symposium on Superconductivity, Kyoto, Miyako Messe, International conference
03 Dec. 2019 - 超伝導熱・磁気顕微鏡の開発を目指して
小久保伸人
Oral presentation, Japanese, ワークショップ「ナノ構造超伝導体における渦糸状態, 大阪府立大学 加藤 勝, 大阪府立大学
02 Jun. 2019 - 超伝導渦糸系のデピ二ングとナノプローブ顕微鏡の開発
小久保伸人
Oral presentation, Japanese, ナノカーボン研究部門2018年度成果報告会 & 電気通信大学ナノトライボロジー研究センター合同研究会, Domestic conference
01 Mar. 2019 - メソズコピック超伝導チャネルに閉じ込めた渦糸ダイナミクス
小久保伸人; R. Besseling; P. H. Kes
Oral presentation, Japanese, 電通大-理科大合同研究会, 電気通信大学ナノトラポロジー研究センター第一回シンポジウム「表面・界面の科学と摩擦」, 電気通信大学, Domestic conference
30 Sep. 2017 - Manipulation of Fluxon States in Microstructured Superconducting Thin Films
Nobuhito Kokubo; Satoru Okayasu; Tsutomu Nojima; Takahiko Sasaki
Poster presentation, English, 10 th international conference on vortex matter in nanostructured superconductors (Vortex X), KU Leuven, Rhodes, Greece, International conference
13 Sep. 2017 - Observation of flux states and interstitial vortices in perforated mesoscopic squares of amorphous superconducting films
M Mitsuishi; K. Kitano; N. Kokubo; S. Okayasu; T. Nojima; T. Sasaki
Poster presentation, English, The 28th International Conference on Low Temperature Physics, Gothenburg, Sweden, http://www.lt28.se/, International conference
10 Aug. 2017 - Flux-flow instability in cleaved thin films of 2H-NbSe2 single crystals
J. Yoshida; H.Ando; N. Kokubo
Poster presentation, English, The 28th International Conference on Low Temperature Physics, Gothenburg, Sweden, http://www.lt28.se/, International conference
10 Aug. 2017 - 小さな超伝導体に閉じ込めた磁束状態の可視化と制御
小久保伸人; 岡安悟; 野島勉; 佐々木孝彦
Invited oral presentation, Japanese, 電通大-理科大合同研究会, ナノトライボロジー研究ステーション, 電気通信大学, Domestic conference
08 Mar. 2017 - Manipulation of Magnetic Flux States in Superconducting Squares with Artificial Pinning Sites
Kohei Kitano; Nobuhito Kokubo; Satoru Okayasu; Tsutomu Nojima; Takahiko Sasaki
Poster presentation, English, 28th International Symposium on Superconductivity, Tokyo, International conference
14 Dec. 2016 - 微細孔をもつ正方形状の微小超伝導体に閉じ込めた磁束状態
小久保伸人; 北野恒平; 望月麟太郎; 岡安悟; 野島勉; 佐々木孝彦
Oral presentation, Japanese, 第24回渦糸物理国内会議, 秋田, Domestic conference
28 Nov. 2016 - 走査SQUID磁気顕微鏡で観測した微小超伝導体の渦糸状態と人工ピン止め
北野恒平; 岡安悟; 野島勉; 佐々木孝彦; 小久保伸人
Poster presentation, Japanese, 日本物理学会2016年秋季大会, 金沢, Domestic conference
15 Sep. 2016 - 人工ピン止めを導入した正方形状の微小超伝導体における渦糸状態
小久保伸人; 北野恒平; 岡安悟; 野島勉; 佐々木孝彦
Oral presentation, Japanese, 日本物理学会2016年秋季大会, 金沢, Domestic conference
14 Sep. 2016 - 異方的渦糸格子の動的融解III
井上俊規; 越智亜玖利; 河村泰樹; 家永紘一郎; 金子真一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会2016年秋季大会, 金沢, Domestic conference
13 Sep. 2016 - NbSe2超伝導体における特異な電流電圧特性と渦糸フローの不安定化
小久保伸人; 宮原大; 岡安悟; 野島勉; 佐々木孝彦
Oral presentation, Japanese, 日本物理学会第71回年次大会, 日本物理学会, 東北学院大学, Domestic conference
21 Mar. 2016 - 異方的渦糸格子の動的融解II
井上俊規; 越智亜玖利; 河村泰樹; 家永紘一郎; 金子真一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会第71回年次大会, 日本物理学会, 東北学院大学, Domestic conference
19 Mar. 2016 - 多重渦状態と殻構造
小久保伸人; 宮原大; 岡安悟; 野島勉
Oral presentation, Japanese, 第23回渦糸物理国内会議, 福岡, Domestic conference
08 Dec. 2015 - Unusual I-V Characteristics and Flux Flow Instability in 2H-NbSe2 Superconductors
Junichiro Yoshida; Nobuhito Kokubo
Poster presentation, English, 28th International Symposium on Superconductivity, ISTEC, Tokyo, International conference
18 Nov. 2015 - Observation of Multi-Vortex States Confined in Mesoscopic Superconductors of Different Geometric Shapes
Nobuhito Kokubo; Satoru Okayasu; Tsutomu Nojima; Takahiko Sasaki
Oral presentation, English, 28th International Symposium on Superconductivity, ISTEC, Tokyo, International conference
18 Nov. 2015 - 周期的微細構造をもつアモルファス超伝導膜に誘起された渦糸状態
北野恒平; 望月麟太郎; 小久保伸人
Poster presentation, Japanese, 日本物理学会2015年秋季大会, 日本物理学会, 関西大学, Domestic conference
19 Sep. 2015 - アンチドット構造をもつ超伝導二層膜に閉じ込めた渦糸状態と電流制御
望月麟太郎; 岡安悟; 野島勉; 佐々木孝彦; 小久保伸人
Poster presentation, Japanese, 日本物理学会2015年秋季大会, 日本物理学会, 関西大学, Domestic conference
19 Sep. 2015 - NbSe2超伝導体における特異な電流電圧特性と渦糸フローの不安定化
吉田純一朗; 小久保伸人
Oral presentation, Japanese, 日本物理学会2015年秋季大会, 日本物理学会, 関西大学, Domestic conference
19 Sep. 2015 - アモルファスNbGe超伝導細線における輸送特性とゆらぎ
佐藤能英瑠; 西脇裕人; 小久保伸人
Oral presentation, Japanese, 第70回日本物理学会年次大会, 日本物理学会, 早稲田大学, Domestic conference
22 Mar. 2015 - 極低温下のパルスモードロック共鳴法による渦糸ダイナミクスの観測II
越智亜玖利; 曽原直也; 小久保伸人; 大熊哲
Oral presentation, Japanese, 第70回日本物理学会年次大会, 日本物理学会, 早稲田大学, Domestic conference
21 Mar. 2015 - Vortex States in Mesoscopic Superconductors
N. Kokubo
Oral presentation, English, Second MIPT-UEC Joint Workshop on Optical Science, University of Electro-Comunications, Tokyo, International conference
20 Oct. 2014 - 超伝導窒化膜の渦糸フローチャネルに閉じ込めた渦糸格子の方位II
山崎史麿; 佐藤能英瑠; 宮原大; 小久保伸人
Oral presentation, Japanese, 日本物理学会2014年秋季大会, 日本物理学会, 中部大学, Domestic conference
08 Sep. 2014 - 三角形状に加工したアモルファスMoGe超伝導膜における量子渦配列の直接観測
宮原大; 岡安悟; 野島勉; 小久保伸人
Oral presentation, Japanese, 日本物理学会2014年秋季大会, 日本物理学会, 中部大学, Domestic conference
08 Sep. 2014 - 極低温下のパルスモードロック共鳴法による渦糸ダイナミクスの観測
越智亜玖利; 曽原直也; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会2014年秋季大会, 日本物理学会, 中部大学, Domestic conference
08 Sep. 2014 - 速度増大による渦糸フローの不安定化とその起源
曽原直也; 越智亜玖利; 金子真一; 小久保伸人
Oral presentation, Japanese, 日本物理学会2014年秋季大会, 日本物理学会, 中部大学, Domestic conference
08 Sep. 2014 - 渦糸フローチャネルで駆動した渦糸格子の方位とサイズ効果
山崎史麿; 佐藤能英瑠; 宮原大; 小久保伸人
Oral presentation, Japanese, 第22 回渦糸物理国内会議, ハイランドふらの, Domestic conference
12 Jul. 2014 - 微小超伝導体の幾何学的形状と量子渦配列
小久保伸人
Oral presentation, Japanese, 第22 回渦糸物理国内会議, ハイランドふらの, Domestic conference
11 Jul. 2014 - 幾何学的に閉じ込められた超伝導量子渦
小久保伸人
Oral presentation, Japanese, 物性研究所短期研究会「スーパーマターが拓く新量子現象」, Invited, Domestic conference
19 Apr. 2014 - 超伝導窒化膜の渦糸フローチャネルに閉じ込めた渦糸格子の方位
山崎史麿; 佐藤能英瑠; 宮原大; 小久保伸人
Oral presentation, Japanese, 日本物理学会第69回年次大会, 日本物理学会, 平塚, Domestic conference
27 Mar. 2014 - パルス法による高速渦糸格子フローの観測と異方性の効果
曽原直也; 長谷圭祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会第69回年次大会, 日本物理学会, 平塚, Domestic conference
27 Mar. 2014 - 速度増大による渦糸格子の再配列と不安定化
越智亜玖利; 長谷圭祐; 曽原直也; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会第69回年次大会, 日本物理学会, 平塚, Domestic conference
27 Mar. 2014 - 三角形状の微小超伝導体における量子渦配列
小久保伸人
Oral presentation, Japanese, 金研共同利用ワークショップ「超伝導体おける渦糸状態の物理と応用(2013)」（第21回渦糸物理国内会議）, 仙台, Domestic conference
14 Dec. 2013 - 走査SQUID顕微鏡で見たアモルファス微小超伝導体の磁束状態
小久保 伸人
Invited oral presentation, Japanese, 日本物理学会 2013年秋季大会, Invited, 日本物理学会, 徳島大学, Domestic conference
27 Sep. 2013 - 高速域における渦糸格子フローの不安定性と再配列
曽原直也; 長谷圭祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会 2013年秋季大会, Domestic conference
27 Sep. 2013 - 電通大「チーム教育（共有教育）」eラーニングでの電磁場概念理解度
阿部浩二; 金長正彦; 小久保伸人; 鈴木勝; 高田亨; 中村仁; 伏屋雄紀
Oral presentation, Japanese, 日本物理学会2013年秋季大会, 日本物理学会, 徳島大学
27 Sep. 2013 - 幾何学的に閉じ込められた磁束量子渦状態II
小久保伸人; 宮原大; 岡安悟; 多持洋孝; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第68回年次大会
Mar. 2013 - 高速駆動した渦糸格子における渦糸間引力II
長谷圭祐; 曽原直也; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第68回年次大会
Mar. 2013 - 正方形状の微小超伝導体における渦糸配列
小久保伸人
Oral presentation, Japanese, 第20回渦糸物理国内会議
Dec. 2012 - 高速駆動した渦糸格子における渦糸間引力
長谷圭祐; 嶋本大祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2012年秋季大会
Sep. 2012 - 幾何学的に閉じ込められた磁束量子渦状態
小久保伸人; 岡安悟; 多持洋孝; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2012年秋季大会
Sep. 2012 - a-NbGe超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転III
小久保伸人; 吉村哲也; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第67回年次大会
Mar. 2012 - Scanning SQUID Microscope Study of Vortex Configurations in Amorphous Superconducting Dots
N. Kokubo
Invited oral presentation, English, Pathbreaking Phase Sciences in Superconductivity 2012, Osaka, International conference
Jan. 2012 - In-Zn-Ga-O 3 次元膜の磁気抵抗、電子局在と熱処理効果II
日高和也; 江崎翔平; 牧瀬圭正; 山田和正; 小久保伸人; 浅野貴行; 篠崎文重; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,第117回九州支部例会
Dec. 2011 - 透明導伝膜In-Sn-Zn-O の輸送特性
鈴川槙一郎; 江崎翔平; 日高和也; 牧瀬圭正; 山田和正; 小久保伸人; 浅野貴行; 篠崎文重; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,第117回九州支部例会
Dec. 2011 - 超伝導細線の温度‐抵抗特性
上原広大; 江崎翔平; 多持洋孝; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第117回九州支部例会
Dec. 2011 - 駆動状態における磁束格子の方位と試料端の形状効果
多持洋孝; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第117回九州支部例会
Dec. 2011 - 駆動速度による渦糸固体の格子方位変化III
嶋本大祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2011年秋季大会
Sep. 2011 - 駆動された磁束格子の方位と試料端の形状効果
多持洋孝; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2011年秋季大会
Sep. 2011 - Reorientation of a moving vortex lattice in oblique magnetic fields
N. Kokubo
Invited oral presentation, English, The 13th International Workshop on Vortex Matter in Superconductors, Chicago, United States of America, International conference
Aug. 2011 - サブＧＨzで捉えた磁束格子フローのモードロック共鳴と形状効果
多持洋孝; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第66回年次大会
Mar. 2011 - 駆動速度による渦糸固体の格子方位変化II
嶋本大祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第66回年次大会
Mar. 2011 - アモルファスMoxGe1-x膜の渦糸状態と次元性
佐藤大樹; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第66回年次大会
Mar. 2011 - a-NbGe超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転III
小久保伸人; 吉村哲也; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第64回年次大会
Mar. 2011 - 超伝導量子渦の幾何学的閉じ込めとピン止め効果
小久保伸人
Invited oral presentation, Japanese, ワークショップ「ナノ構造超伝導体における渦糸状態」
Jan. 2011 - (In2O3)1−x(ZnO)x 膜の超伝導特性III
高田聡; 篠崎文重; 山田和正; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - アモルファス超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転II
吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部
Dec. 2010 - 超伝導/微小強磁性複合構造における臨界電流と磁束フロー
多持洋孝; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - In-Zn-Ga-O ３次元膜の磁気抵抗, 電子局在と熱処理効果
江崎翔平; 牧瀬圭正; 山田和正; 小久保伸人; 篠崎文重; 笘井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - (In2O3)1−x(ZnO)x 膜の超伝導特性III
高田聡; 篠崎文重; 山田和正; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - FIB 法により作成された擬一次元In/Mo 超伝導体の輸送特性
田崎茂; 江崎翔平; 牧瀬圭正; 山田和正; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - アモルファスNbGe 超伝導膜における臨界電流と形状効果
尾堂智隆; 多持洋孝; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - a-NbGe 超伝導膜における磁束格子フローと磁気相図
下岡孝明; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 2,3 次元In2O3-ZnO 膜の磁気抵抗に及ぼす熱処理効果
日高和也; 江崎翔平; 牧瀬圭正; 山田和正; 小久保伸人; 篠崎文重; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 導電性高分子ポリアニリン膜の抵抗率・キャリア数の温度依存性
滝川陽介; 山田和正; 小久保伸人; 篠崎文重; 板東徹; 黒田憲寛; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 延伸された高分子ポリアニリン膜の電気輸送特性
源島久志; 滝川陽介; 山田和正; 小久保伸人; 篠崎文重; 安田剛; 坂東徹; 黒田憲寛; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 導電性高分子膜におけるゼーベック係数のドーパント量依存性
成清敬史; 滝川陽介; 山田和正; 小久保伸人; 篠崎文重; 坂東徹; 黒田憲寛; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 多結晶酸化物半導体In2O3-ZnO の有効ホール移動度と結晶粒界
松本直樹; 山田和正; 小久保伸人; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第116回日本物理学会九州支部例会
Dec. 2010 - 走査型SQUID顕微鏡で直接観測した微小超伝導体の磁束配列
小久保伸人; 岡安悟; 神田晶申; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2010年秋季大会
Sep. 2010 - 超伝導体/微小強磁性複合構造における磁束フロー
多持洋考; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2010年秋季大会
Sep. 2010 - a-NbGe超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転II
吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2010年秋季大会
Sep. 2010 - 駆動速度による渦糸固体の格子方位変化
嶋本大祐; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2010年秋季大会
Sep. 2010 - 回転駆動された渦糸格子リングの微視的構造変化II
松村有夏; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2010年秋季大会
Sep. 2010 - SQUID 顕微鏡で直接観測した微小超伝導体の磁束配列
小久保伸人
Invited oral presentation, Japanese, 日本物理学会第65回年次大会(シンポジウム)
Mar. 2010 - アモルファス超伝導体/微小強磁性複合構造における磁束フローチャネル
多持洋考; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第65回年次大会
Mar. 2010 - a-NbGe超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転
吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第65回年次大会
Mar. 2010 - 渦糸固体の動的量子融解と格子のフロー状態II
大熊哲; 今泉広基; 嶋本大祐; 小久保伸人
Oral presentation, Japanese, 日本物理学会,第65回年次大会
Mar. 2010 - 回転駆動された渦糸格子リングの微視的構造変化
松村有夏; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第65回年次大会
Mar. 2010 - (In2O3)1−x(ZnO)x 膜の超伝導特性II
高田聡; 山田和正; 篠崎文重; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - SiO2 基板上In/Ge 薄膜の超伝導特性
田崎茂; 松原洋祐; 牧瀬圭正; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - (In2O3)1−x(ZnO)x 膜の超伝導特性II
高田聡; 山田和正; 篠崎文重; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - 簡易温度可変インサートの作製とFeSe 系超伝導体のR-T 特性
村上里奈; 多持洋孝; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - FIB 加工により作成したIn/Mo 細線の超伝導特性
松原洋祐; 田崎茂; 牧瀬圭正; 山田和正; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - アモルファス超伝導体/微小強磁性複合構造における磁束フローと臨界電流
多持洋考; 吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 第115回日本物理学会九州支部例会
Dec. 2009 - アモルファス超伝導膜の傾斜磁場下における磁束格子フローの格子方位回転
吉村哲也; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - 導電性高分子ポリアニリン膜のホール効果・ゼーベック効果
滝川陽介; 山田和正; 小久保伸人; 篠崎文重; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,第115回日本物理学会九州支部例会
Dec. 2009 - 傾斜磁場下における磁束格子フローの格子回転
小久保伸人
Oral presentation, Japanese, 第１７回磁束線物理国内会議,第１７回磁束線物理国内会議
Dec. 2009 - アモルファスNbGe膜におけるモードロック共鳴
小久保伸人; 吉村哲也; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Dec. 2009 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導III
高田聡; 山口高史; 山田和正; 篠崎文重; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - Direct Observation of Vortex States in Amorphous MoGe Disks by Scanning SQUID Microscopy
N. Kokubo; S. Okayasu; A. Kanda; B. Shinozaki
Invited oral presentation, English, The 12th International Workshop on Vortex Matter in Superconductors, Yamanashi, International conference
Sep. 2009 - 走査型SQUID顕微鏡で直接観測したアモルファスMoGe円板の磁束状態
小久保伸人; 岡安悟; 神田晶申; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - 渦糸固体の動的量子融解と格子のフロー状態
今泉広基; 松村有夏; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - 回転駆動された渦糸格子リングIII
松村有夏; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導III
高田聡; 山口高史; 山田和正; 篠崎文重; 小久保伸人; 牧瀬圭正; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - 低次元(1D or 2D)In/Moの超伝導特性
松原洋祐; 田崎茂; 牧瀬圭正; 山田和正; 小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2009年秋季大会
Sep. 2009 - Periodic spacing and lattice orientations of driven vortex matter in amorphous MoGe films detected by mode locking techniques
N. Kokubo; T. Nishizaki; B. Shinizaki; P. H. Kes
Invited oral presentation, English, Joint JSPS-ESF International Conference on Nanoscience and Engineering in Superconductivity, Ibaraki, International conference
Mar. 2009 - モードロック共鳴による磁束格子フローの格子方位と交流駆動依存性
小久保伸人; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第64回年次大会
Mar. 2009 - 渦糸固体の動的量子融解III
今泉広基; 松村有夏; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第64回年次大会
Mar. 2009 - polycrystalline In2O3-ZnO膜のEELS観察と輸送特性
牧瀬圭正; 三石和貴; 古屋一夫; 山口高史; 高田聡; 小倉俊助; 小久保伸人; 山田和正; 篠崎文重; 笘井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,第64回年次大会
Mar. 2009 - In・Sb/Mo膜の伝導特性
小早川優介; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第64回年次大会
Mar. 2009 - (In2O3)1−x(ZnO)x膜の超伝導特性
高田聡; 山口高史; 小倉俊介; 小久保伸人; 山田和正; 篠崎文重; 牧瀬圭正; 寺井恒太; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - 駆動された渦糸格子の格子方位
小久保伸人; 西嵜照和; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 第16回渦糸物理国内会議,第16回渦糸物理国内会議
Dec. 2008 - アモルファス膜における秩序―無秩序転移と動的量子融解
大熊哲; 今泉広基; 鈴木啓久; 小久保伸人
Oral presentation, Japanese, 第16回渦糸物理国内会議,第16回渦糸物理国内会議
Dec. 2008 - コルビノディスク内で回転駆動された渦糸格子リング
山崎祐介; 小久保伸人; 大熊哲
Oral presentation, Japanese, 第16回渦糸物理国内会議,第16回渦糸物理国内会議
Dec. 2008 - 磁束格子フローの格子方位と交流駆動
小久保伸人; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - グラファイトの磁気抵抗2
小倉俊介; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - In・Sb/Mo 膜の伝導特性
小早川優介; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - (In2O3)1－x(ZnO)x膜の熱処理効果と輸送特性
山口高史; 高田聡; 小倉俊介; 小久保伸人; 山田和正; 篠崎文重; 牧瀬圭正; 寺井恒太; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - (In2O3)1−x(ZnO)x膜の超伝導特性
高田聡; 山口高史; 小倉俊介; 小久保伸人; 山田和正; 篠崎文重; 牧瀬圭正; 寺井恒太; 苫井重和; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会九州支部,114回日本物理学会九州支部例会
Dec. 2008 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導 II
山口高史; 高田聡; 小倉俊助; 小久保伸人; 牧瀬圭正; 山田和正; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - モードロック共鳴と磁束格子運動の結晶方位III
小久保伸人; 西嵜照和; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導 II
山口高史; 高田聡; 小倉俊助; 小久保伸人; 牧瀬圭正; 山田和正; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - InO-ZnO膜の微細構造と輸送特性
牧瀬圭正; 三石和貴; 古屋一夫; 山口高史; 高田聡; 小倉俊助; 小久保伸人; 山田和正; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - 理系新入生の物理基礎学力変化
武田信一; 篠崎文重; 小久保伸人; 藤井新一郎; 藤原智子
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - モードロック共鳴と広帯域ノイズIII
井上甚; 今泉広基; 市村拓也; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - アモルファスMoxGe1-x膜渦糸固体相における秩序－無秩序転移II
鈴木啓久; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - 渦糸固体の動的量子融解II
今泉広基; 鈴木啓久; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - 回転駆動された渦糸格子リングII
山崎祐介; 井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2008年秋季大会
Sep. 2008 - InO-ZnO薄膜の超伝導特性と微細構造
牧瀬圭正; 三石和貴; 古屋一夫; 山口高史; 高田聡; 小倉俊助; 篠崎文重; 小久保伸人; 矢野公規; 中村浩昭; 山田和正
Oral presentation, Japanese, 応用物理学会,第69回応用物理学会学術講演会
Sep. 2008 - 高抵抗In2O3-ZnO微結晶膜のホール効果測定
山田和正; 山口高史; 小久保伸人; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 応用物理学会,第69回応用物理学会学術講演会
Sep. 2008 - Hall Effect and Fluctuations in Amorphous Nb3Ge Films
N. Kokubo; J. Aarts; P. H. Kes
Invited oral presentation, English, The Joint Vortex-Physics and ESF-Vortex Matter Workshop, Lunteren, Netherlands, International conference
Aug. 2008 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導
高田聡; 山口高史; 小久保伸人; 牧瀬圭正; 山田和正; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - Indium Zinc Oxideの光伝導
山田和正; 山口高史; 小久保伸人; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 応用物理学関連連合,第55回応用物理学関連連合講演会
Mar. 2008 - モードロック共鳴と磁束格子運動の結晶方位II
小久保伸人; 西嵜照和; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - 低キャリア多結晶(In2O3)1−x(ZnO)x膜の超伝導
高田聡; 山口高史; 小久保伸人; 牧瀬圭正; 山田和正; 篠崎文重; 矢野公規; 中村浩昭
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - Ge/In多層膜における超伝導・絶縁体相の輸送特性
谷岡肇; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - モードロック共鳴と広帯域ノイズII
井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - アモルファスMoxGe1-x膜渦糸固体相における秩序－無秩序転移
鈴木啓久; 神代賢一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - 渦糸固体の動的量子融解
大熊哲; 鈴木賢一; 井上甚; 今泉広基; 小久保伸人
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - 回転駆動された渦糸格子リング
山崎祐介; 鈴木啓久; 井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第63回年次大会
Mar. 2008 - Lattice orientations of driven vortex matter detected by mode locking techniques
N. Kokubo; T. Nishizaki; B. Shinizaki; P. H. Kes
Invited oral presentation, English, The 4th CREST Nano-Virtual-Labs Joint Workshop on Superconductivity : Critical Current (NVLS2007-CC), Kitakyushu, International conference
Dec. 2007 - モードロック共鳴と磁束格子運動の結晶方位
小久保伸人; 西嵜照和; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 日本物理学会九州支部,113回日本物理学会九州支部例会
Dec. 2007 - Ge/In 多層膜の超伝導特性
谷岡肇; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,113回日本物理学会九州支部例会
Dec. 2007 - In・Sb/Mo 膜の超伝導特性
小早川優介; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,113回日本物理学会九州支部例会
Dec. 2007 - 低キャリアIn2O3-ZnO 膜の輸送特性
篠崎文重; 船木誠; 牧瀬圭正; 山口高志; 小久保伸人; 山田和正
Oral presentation, Japanese, 日本物理学会九州支部,113回日本物理学会九州支部例会
Dec. 2007 - グラファイトの磁気抵抗
小倉俊介; 小久保伸人; 山田和正; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,113回日本物理学会九州支部例会
Dec. 2007 - Mode locking and vortex dynamics in mesoscopic flow channels
N. Kokubo
Invited oral presentation, English, 2nd International Autumn Seminar on Nanoscience and Engineering in Superconductivity for Young Scientists, Tochigi, International conference
Nov. 2007 - モードロック共鳴による磁束格子フローの結晶方位
小久保伸人
Invited oral presentation, Japanese, 東北大学金属材料研究所ワークショップ“ナノ構造超伝導体とその応用”
Nov. 2007 - Mode locking and lattice orientations of vortex matter in amorphous MoGe films
N. Kokubo; B. Shinozaki; P.H. Kes
Invited oral presentation, English, Joint JSPS and ESF Conference on Vortex Matter in Nanostructured Superconductors (Vortex V), Rhodes, Greece, International conference
Sep. 2007 - アモルファスMoGe膜における駆動された磁束格子の結晶方位転移
小久保伸人; 篠崎文重; P. H. Kes
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - モードロック共鳴と広帯域ノイズ
井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - 渦糸固体相における渦糸ダイナミクスとエッジの影響
神代賢一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - 回転駆動させた渦糸固体のダイナミクスとサイズ効果
山崎祐介; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - 超伝導－絶縁体転移近傍でのアモルファスGa超薄膜の電気輸送特性
牧瀬圭正; 小倉俊助; 谷岡肇; 小久保伸人; 篠崎文重; 川口尚
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - 新指導要領による入学生の変化と物理教育の状況について
武田信一; 篠崎文重; 吉田英智; 小久保伸人
Oral presentation, Japanese, 日本物理学会,第62回年次大会
Sep. 2007 - 平成17 年度～平成19 年度九州大学・理系入学生の物理基礎学力調査
篠崎文重; 武田信一; 吉田英智; 小久保伸人
Oral presentation, Japanese, 九州地区一般教育協議会,九州地区一般教育協議会
Sep. 2007 - アモルファスＭｏＧｅ膜における磁束格子のモードロック共鳴と動的秩序化
小久保伸人; 門脇和男
Oral presentation, Japanese, 第３回「超伝導ナノサイエンスと応用」研究会
Mar. 2007 - 金属/グラファイトの超伝導
小久保伸人; 高本信太郎; 牧瀬圭正; 篠崎文重
Oral presentation, Japanese, 日本物理学会,2007年春季大会
Mar. 2007 - 磁束フローチャネルにおけるつり合い効果と動的フロー構造
小久保伸人; R. Besseling; P. H. Kes
Oral presentation, Japanese, 日本物理学会,2007年春季大会
Mar. 2007 - モードロックされた渦糸フローと電圧ノイズ II
井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2007年春季大会
Mar. 2007 - アモルファスMoxGe1-x膜の渦糸固体相における渦糸ダイナミクス
神代賢一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2007年春季大会
Mar. 2007 - 金属/グラファイトの超伝導
小久保伸人; 高本信太郎; 篠崎文重
Oral presentation, Japanese, 日本物理学会九州支部,第112回日本物理学会九州支部例会
Dec. 2006 - 磁束フローチャネルにおける動的スリップ転移
小久保伸人; T. G. Sorop; R. Besseling; P. H. Kes
Oral presentation, Japanese, 日本物理学会,2006年秋季大会
Sep. 2006 - モードロックされた渦糸フローと電圧ノイズ
井上甚; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2006年秋季大会
Sep. 2006 - 極低温域におけるピーク効果
神代賢一; 小久保伸人; 大熊哲
Oral presentation, Japanese, 日本物理学会,2006年秋季大会
Sep. 2006 - Peak effect and mode locking of vortex matter in NbSe2 crystals
N. Kokubo; K. Kadowaki; K. Takita; T. G. Sorop; P. H. Kes
Invited oral presentation, English, 11th International Workshop on Vortex Matter, Wroclaw, Poland, International conference
Jul. 2006 - Quasi One-Dimensional Vortex Flow Driven Through Mesoscopic Channels
N. Kokubo; R. Besseling; T.G. Sorop; P. H. Kes
Invited oral presentation, English, 10th Vortex state studies workshop, Mumbai, India, International conference
Jan. 2005 - Dynamic ordering and flow structure of vortex matter driven through mesoscopic channels
N. Kokubo; R. Besseling; P. H. Kes
Invited oral presentation, English, The Joint 9th International Workshop on Vortex Dynamics and Vortex Matter (ESF), Oléron Island France, International conference
Jun. 2003 - Mode locking of the Abrikosov vortex lattice driven through mesoscopic channels
N. Kokubo; R. Besseling; P. H. Kes
Invited oral presentation, English, ESF workshop, Vortices in Josephson Junctions and Nanostructures, Maratea, Italy, International conference
Sep. 2002 - Mode locking for ac dc driven vortices in easy flow channels
N. Kokubo; R. Besseling; P. H. Kes
Invited oral presentation, English, 8th Workshop on Vortex Physics, Bariloche, Argentina, International conference
Nov. 2001
Research Themes
- 先端型ナノSQUIDを用いた局所温度計測技術の開発
精密測定技術振興財団, Principal investigator
Jan. 2024 - Mar. 2025 - 針状のガラス管先端を利用した超伝導ナノセンシング技術の開発
01 Apr. 2021 - ナノピペットを利用した超伝導ナノセンシング技術の開発
公益財団法人精密測定技術振興財団, 研究助成
01 Apr. 2020 - 微小な超伝導単結晶薄膜に閉じ込めた量子渦状態と制御
小久保伸人
Principal investigator
01 Apr. 2017 - 31 Mar. 2019 - ナノドットを用いた微小超伝導体の反量子渦状態と制御
小久保伸人
Principal investigator
01 Apr. 2014 - 31 Mar. 2017 - 超伝導量子渦ビットの創出
Nobuhito KOKUBO
Principal investigator
01 Apr. 2014 - 31 Mar. 2016 - Novel ordered phases at low temperatures and dynamic phase transitions in the superconducting vortex system
Okuma Satoshi; KOKUBO Nobuhito; ISHIDA Takekazu
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Tokyo Institute of Technology, Grant-in-Aid for Scientific Research (B), We have developed a measurement system for a mode-locking resonance with pulsed currents that generate much less heat (by three orders of magnitude) than the previous one, which enables to detect the flow of fast driven vortex lattices. By employing it at low temperatures down to 0.05 K, we successfully observe the dynamic quantum melting of driven lattice in the limit of zero pinning. Thus, we complete static vortex phase diagrams at nearly zero temperature as a function of applied field, namely, the phase diagrams of the field-induced quantum phase transition simultaneously in the absence and presence of pinning. Also, we have performed studies on the reversible-to-irreversible flow transition (RIT) and obtained the following new results: We acquire information on the vortex configuration in the vicinity of RIT. Also, we observe the critical behavior of RIT in the translational motion system where only the local ac shear due to strong random pinning is present., 25287084
01 Apr. 2013 - 31 Mar. 2016 - 幾何学的に閉じ込められた磁束量子状態
01 Apr. 2011 - 31 Mar. 2015 - 磁束格子フローの結晶方位
2008 - 2009 - 微細探針を用いた走査型SQUID顕微鏡センシングコイルによる空間分解能向上の研究
岡安悟
2005 - 2006 - メゾスコピック磁束フローチャネルを用いた整流デバイスの研究
2004 - 2005
