Feb. 2025 - Present
The University of Electro-Communications, Graduate School of Informatics and Engineering, 准教授, Japan

Apr. 2017 - Jan. 2025
The University of Tokyo, The Graduate School of Engineering, Research associate

Apr. 2016 - Mar. 2017
The University of Tokyo, The Institute for Solid State Physics, Postdoctral researcher

Dimensionality-driven power-law gap in the bilayer TaTe2 grown by molecular-beam epitaxy
Bruno Kenichi Saika; Satoshi Yoshida; Markel Pardo-Almanza; Natsuki Mitsuishi; Masato Sakano; Yuita Fujisawa; Yue Wang; Yoshihiro Iwasa; Hideki Matsuoka; Hidefumi Takahashi; Shintaro Ishiwata; Yoshinori Okada; Masaki Nakano; Kyoko Ishizaka
APL Materials, AIP Publishing, 12, 7, 01 Jul. 2024, Reducing dimensionality can induce profound modifications to the physical properties of a system. In two-dimensional TaS2 and TaSe2, the charge-density wave phase accompanies a Mott transition, thus realizing the strongly correlated insulating state. However, this scenario deviates from TaTe2 due to p–d hybridization, resulting in a substantial contribution of Te 5p at the Fermi level. Here, we show that, differently from the Mott insulating phase of its sister compounds, bilayer TaTe2 hosts a power-law (V-shaped) gap at the Fermi level reminiscent of a Coulomb gap. It suggests the possible role of unscreened long-range Coulomb interactions emerging in lowered dimensions, potentially coupled with a disordered short-range charge-density wave. Our findings reveal the importance of long-range interactions sensitive to interlayer screening, providing another venue for the interplay of complex quantum phenomena in two-dimensional materials.
Scientific journal

180 °-twisted bilayer ReSe2 as an artificial noncentrosymmetric semiconductor
S. Akatsuka; M. Sakano; T. Yamamoto; T. Nomoto; R. Arita; R. Murata; T. Sasagawa; K. Watanabe; T. Taniguchi; N. Mitsuishi; M. Kitamura; K. Horiba; K. Sugawara; S. Souma; T. Sato; H. Kumigashira; K. Shinokita; H. Wang; K. Matsuda; S. Masubuchi; T. Machida; K. Ishizaka
Physical Review Research, 03 Jun. 2024
Scientific journal

Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe2
Natsuki Mitsuishi; Yusuke Sugita; Tomoki Akiba; Yuki Takahashi; Masato Sakano; Koji Horiba; Hiroshi Kumigashira; Hidefumi Takahashi; Shintaro Ishiwata; Yukitoshi Motome; Kyoko Ishizaka
Physical Review Research, 09 Feb. 2024
Scientific journal

Ultrafast control of the crystal structure in a topological charge-density-wave material
Takeshi Suzuki; Yuya Kubota; Natsuki Mitsuishi; Shunsuke Akatsuka; Jumpei Koga; Masato Sakano; Satoru Masubuchi; Yoshikazu Tanaka; Tadashi Togashi; Hiroyuki Ohsumi; Kenji Tamasaku; Makina Yabashi; Hidefumi Takahashi; Shintaro Ishiwata; Tomoki Machida; Iwao Matsuda; Kyoko Ishizaka; Kozo Okazaki
Physical Review B, 22 Nov. 2023
Scientific journal, English

Symmetry Engineering in Twisted Bilayer WTe₂
Yijin Zhang; Keisuke Kamiya; Takato Yamamoto; Masato Sakano; Xiaohan Yang; Satoru Masubuchi; Shota Okazaki; Keisuke Shinokita; Tongmin Chen; Kohei Aso; Yukiko Yamada-Takamura; Yoshifumi Oshima; Kenji Watanabe; Takashi Taniguchi; Kazunari Matsuda; Takao Sasagawa; Kyoko Ishizaka; Tomoki Machida
Nano Letters, 25 Oct. 2023
Scientific journal, English

Charge transport and thermopower in the electron-doped narrow gap semiconductor Ca1−xLaxPd3O4
Kouta Kazama; Masato Sakano; Kohei Yamagami; Takuo Ohkochi; Kyoko Ishizaka; Terumasa Tadano; Yusuke Kozuka; Hidetoshi Yoshizawa; Yoshihiro Tsujimoto; Kazunari Yamaura; Jun Fujioka
Physical Review Materials, 11 Aug. 2023
Scientific journal, English

Signature of topological band crossing in ferromagnetic Cr1/3NbSe2 epitaxial thin film
Bruno SAIKA; Satoshi Hamao; Yuki Majima; Xiang Huang; Hideki Matsuoka; Satoshi Yoshida; Miho Kitamura; Masato Sakano; Tatsuto Hatanaka; Takuya Nomoto; Motoaki Hirayama; Koji Horiba; Hiroshi KUMIGASHIRA; Ryotaro Arita; Yoshihiro Iwasa; Masaki Nakano; Kyoko Ishizaka
Physical Review Research, 04 Nov. 2022
Scientific journal, English

Dry pick-and-flip assembly of van der Waals heterostructures for microfocus angle-resolved photoemission spectroscopy
Satoru Masubuchi; Masato Sakano; Yuma Tanaka; Yusai Wakafuji; Takato Yamamoto; Shota Okazaki; Kenji Watanabe; Takashi Taniguchi; Jincai Li; Hirotaka Ejima; Takao Sasagawa; Kyoko Ishizaka; Tomoki Machida
Scientific Reports, 29 Jun. 2022, AbstractWe present a dry pick-and-flip assembly technique for angle-resolved photoemission spectroscopy (ARPES) of van der Waals heterostructures. By combining Elvacite2552C acrylic resin and 1-ethyl-3-methylimidazolium ionic liquid, we prepared polymers with glass transition temperatures (Tg) ranging from 37 to 100 ℃. The adhesion of the polymer to the 2D crystals was enhanced at $${T}_{\text{g } }$$

T
g

. By utilizing the difference in $${T}_{\text{g } }$$

T
g

, a 2D heterostructure can be transferred from a high-$${T}_{\text{g } }$$

T
g

polymer to a lower-$${T}_{\text{g } }$$

T
g

polymer, which enables flipping its surface upside down. This process is suitable for assembling heterostructures for ARPES, where the top capping layer should be monolayer graphene. The laser-based micro-focused ARPES measurements of 5-layer WTe2, 3-layer MoTe2, 2-layer WTe2/few-layer Cr2Ge2Te6, and twisted double bilayer WTe2 demonstrate that this process can be utilized as a versatile sample fabrication method for investigating the energy spectra of 2D heterostructures.
Scientific journal, English

Odd-even layer-number effect of valence-band spin splitting in WTe2
Masato Sakano; Yuma Tanaka; Satoru Masubuchi; Shota Okazaki; Takuya Nomoto; Atsushi Oshima; Kenji Watanabe; Takashi Taniguchi; Ryotaro Arita; Takao Sasagawa; Tomoki Machida; Kyoko Ishizaka
Physical Review Research, 27 Jun. 2022
Scientific journal, English

顕微レーザー角度分解光電子分光による原子層WTe₂フレークの電子状態の観測
昌人 坂野; 香子 石坂; 覚 増渕; 友樹 町田
応用物理, 01 Nov. 2021
Scientific journal, Japanese

Enhanced Thermopower in the Antiferromagnetic Phase of Mn_2−xCr_xSb
Kurea Nakagawa; Yu Miyazaki; Natsuki Mitsuishi; Masato Sakano; Tomoyuki Yokouchi; Kyoko Ishizaka; Yuki Shiomi
Journal of the Physical Society of Japan, 15 Dec. 2020
Scientific journal, English

Competing spin modulations in the magnetically frustrated semimetal EuCuSb
Hidefumi Takahashi; Kai Aono; Yusuke Nambu; Ryoji Kiyanagi; Takuya Nomoto; Masato Sakano; Kyoko Ishizaka; Ryotaro Arita; Shintaro Ishiwata
Physical Review B, 13 Nov. 2020
Scientific journal, English

Publisher Correction: A weak topological insulator state in quasi-one-dimensional bismuth iodide
Ryo Noguchi; T. Takahashi; K. Kuroda; M. Ochi; T. Shirasawa; M. Sakano; C. Bareille; M. Nakayama; M. D. Watson; K. Yaji; A. Harasawa; H. Iwasawa; P. Dudin; T. K. Kim; M. Hoesch; V. Kandyba; A. Giampietri; A. Barinov; S. Shin; R. Arita; T. Sasagawa; Takeshi Kondo
Nature, 06 Aug. 2020
Scientific journal, English

Switching of band inversion and topological surface states by charge density wave
Natsuki Mitsuishi; Y. Sugita; Mohammad Saeed Bahramy; M. Kamitani; Tatsuya Sonobe; M. Sakano; T. Shimojima; H. Takahashi; Hideaki Sakai; K. Horiba; H. Kumigashira; K. Taguchi; K. Miyamoto; Taichi Okuda; Shintaro Ishiwata; Yukitoshi Motome; Kyoko Ishizaka
Nature Communications, 18 May 2020, AbstractTopologically nontrivial materials host protected edge states associated with the bulk band inversion through the bulk-edge correspondence. Manipulating such edge states is highly desired for developing new functions and devices practically using their dissipation-less nature and spin-momentum locking. Here we introduce a transition-metal dichalcogenide VTe2, that hosts a charge density wave (CDW) coupled with the band inversion involving V3d and Te5p orbitals. Spin- and angle-resolved photoemission spectroscopy with first-principles calculations reveal the huge anisotropic modification of the bulk electronic structure by the CDW formation, accompanying the selective disappearance of Dirac-type spin-polarized topological surface states that exist in the normal state. Thorough three dimensional investigation of bulk states indicates that the corresponding band inversion at the Brillouin zone boundary dissolves upon the CDW formation, by transforming into anomalous flat bands. Our finding provides a new insight to the topological manipulation of matters by utilizing CDWs’ flexible characters to external stimuli.
Scientific journal, English

Hybridization between the ligand p band and Fe−3d orbitals in the p-type ferromagnetic semiconductor (Ga,Fe)Sb
Takahito Takeda; Masahiro Suzuki; Le Duc Anh; Nguyen Thanh Tu; Thorsten Schmitt; Satoshi Yoshida; Masato Sakano; Kyoko Ishizaka; Yukiharu Takeda; Shin-ichi Fijimori; Munetoshi Seki; Hitoshi Tabata; Atsushi Fujimori; Vladimir N. Strocov; Masaaki Tanaka; Masaki Kobayashi
Physical Review B, 28 Apr. 2020
Scientific journal, English

Radial Spin Texture in Elemental Tellurium with Chiral Crystal Structure
M. Sakano; M. Hirayama; T. Takahashi; S. Akebi; M. Nakayama; K. Kuroda; K. Taguchi; T. Yoshikawa; K. Miyamoto; T. Okuda; K. Ono; H. Kumigashira; Toshiya Ideue; Y. Iwasa; N. Mitsuishi; K. Ishizaka; S. Shin; Takashi Miyake; S. Murakami; T. Sasagawa; Takeshi Kondo
Physical Review Letters, 30 Mar. 2020
Scientific journal, English

Evolution of Electronic States and Emergence of Superconductivity in the Polar Semiconductor GeTe by Doping Valence-Skipping Indium
Markus Kriener; M. Sakano; M. Kamitani; M. S. Bahramy; R. Yukawa; K. Horiba; H. Kumigashira; K. Ishizaka; Y. Tokura; Y. Taguchi
Physical Review Letters, 31 Jan. 2020
Scientific journal, English

Intrinsic 2D Ferromagnetism in V₅Se₈ Epitaxial Thin Films
Masaki Nakano; Yue Wang; Satoshi Yoshida; Hideki Matsuoka; Yuki Majima; Keisuke Ikeda; Yasuyuki Hirata; Yukiharu Takeda; Hiroki Wadati; Yoshimitsu Kohama; Yuta Ohigashi; Masato Sakano; Kyoko Ishizaka; Yoshihiro Iwasa
Nano Letters, 11 Dec. 2019
Scientific journal, English

Gigahertz-repetition-rate, narrowband-deep-ultraviolet light source for minimization of acquisition time in high-resolution angle-resolved photoemission spectroscopy
Kosuke Yoshioka; J. Omachi; M. Sakano; T. Shimojima; K. Ishizaka; M. Kuwata-Gonokami
Review of Scientific Instruments, 01 Dec. 2019, Ultrahigh-repetition-rate (1.1 GHz), deep-ultraviolet coherent light at 208.8 nm is generated by applying an external Fabry–Pérot cavity for repetition-rate multiplication to the fourth harmonics of a 10-ps, mode-locked Ti:sapphire laser. Its small pulse energy minimizes the unwanted space charge effect, while its high repetition rate drastically reduces the acquisition time in high-energy resolution angle-resolved photoemission spectroscopy using hemispherical electron analyzers. The absence of the space charge effect in the photoemission spectrum near the Fermi edge of polycrystalline Au at 8 K demonstrates this idea.
Scientific journal, English

Strongly anisotropic high-temperature Fermi surface of the Kondo semimetal CeNiSn revealed by angle-resolved photoemission spectroscopy
Cédric Bareille; T.-S. Nam; Toshiro Takabatake; Kenta Kuroda; Takeshi Yajima; Mitsuhiro Nakayama; So Kunisada; Shuntaro Akebi; Masato Sakano; Shunsuke Sakuragi; Ryo Noguchi; Byung Il Min; Shik Shin; Takeshi Kondo
Physical Review B, 23 Jul. 2019
Scientific journal, English

A weak topological insulator state in quasi-one-dimensional bismuth iodide
Ryo Noguchi; T. Takahashi; K. Kuroda; M. Ochi; T. Shirasawa; M. Sakano; C. Bareille; M. Nakayama; M. D. Watson; K. Yaji; A. Harasawa; H. Iwasawa; P. Dudin; T. K. Kim; M. Hoesch; V. Kandyba; A. Giampietri; A. Barinov; S. Shin; R. Arita; T. Sasagawa; Takeshi Kondo
Nature, Feb. 2019
Scientific journal, English

Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2
M. Sakano; M. S. Bahramy; H. Tsuji; I. Araya; K. Ikeura; H. Sakai; S. Ishiwata; K. Yaji; K. Kuroda; A. Harasawa; S. Shin; K. Ishizaka
Physical Review B, 01 Mar. 2017
Scientific journal, English

Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states
Ryo Noguchi; Kenta Kuroda; K. Yaji; K. Kobayashi; M. Sakano; A. Harasawa; Takeshi Kondo; F. Komori; S. Shin
Physical Review B, 24 Jan. 2017
Scientific journal, English

Momentum-dependent sign inversion of orbital order in superconducting FeSe
Y. Suzuki; T. Shimojima; T. Sonobe; A. Nakamura; M. Sakano; H. Tsuji; J. Omachi; K. Yoshioka; M. Kuwata-Gonokami; T. Watashige; R. Kobayashi; S. Kasahara; T. Shibauchi; Y. Matsuda; Y. Yamakawa; H. Kontani; K. Ishizaka
Physical Review B, 13 Nov. 2015
Scientific journal, English

Topologically protected surface states in a centrosymmetric superconductor β-PdBi2
M. Sakano; K. Okawa; M. Kanou; H. Sanjo; T. Okuda; T. Sasagawa; K Ishizaka
Nature Communications, 13 Oct. 2015, AbstractThe topological aspects of electrons in solids can emerge in real materials, as represented by topological insulators. In theory, they show a variety of new magneto-electric phenomena, and especially the ones hosting superconductivity are strongly desired as candidates for topological superconductors. While efforts have been made to develop possible topological superconductors by introducing carriers into topological insulators, those exhibiting indisputable superconductivity free from inhomogeneity are very few. Here we report on the observation of topologically protected surface states in a centrosymmetric layered superconductor, β-PdBi2, by utilizing spin- and angle-resolved photoemission spectroscopy. Besides the bulk bands, several surface bands are clearly observed with symmetrically allowed in-plane spin polarizations, some of which crossing the Fermi level. These surface states are precisely evaluated to be topological, based on the Z2 invariant analysis in analogy to three-dimensional strong topological insulators. β-PdBi2 may offer a solid stage to investigate the topological aspect in the superconducting condensate.
Scientific journal, English

Lifting ofxz/yzorbital degeneracy at the structural transition in detwinned FeSe
T. Shimojima; Y. Suzuki; T. Sonobe; A. Nakamura; M. Sakano; J. Omachi; K. Yoshioka; M. Kuwata-Gonokami; K. Ono; H. Kumigashira; A. E. Böhmer; F. Hardy; T. Wolf; C. Meingast; H. v. Löhneysen; H. Ikeda; K. Ishizaka
Physical Review B, 29 Sep. 2014
Scientific journal, English

Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry
Ryuji Suzuki; M. Sakano; Y. J. Zhang; R. Akashi; D. Morikawa; A. Harasawa; K. Yaji; K. Kuroda; K. Miyamoto; T. Okuda; K. Ishizaka; R. Arita; Y. Iwasa
Nature Nanotechnology, Aug. 2014
Scientific journal, English

Strongly Spin-Orbit Coupled Two-Dimensional Electron Gas Emerging near the Surface of Polar Semiconductors
M. Sakano; M. S. Bahramy; A. Katayama; T. Shimojima; H. Murakawa; Y. Kaneko; W. Malaeb; S. Shin; K. Ono; H. Kumigashira; R. Arita; N. Nagaosa; H. Y. Hwang; Y. Tokura; K. Ishizaka
Physical Review Letters, 07 Mar. 2013
Scientific journal, English

Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting
M. Sakano; J. Miyawaki; A. Chainani; Y. Takata; T. Sonobe; T. Shimojima; M. Oura; S. Shin; M. S. Bahramy; R. Arita; N. Nagaosa; H. Murakawa; Y. Kaneko; Y. Tokura; K. Ishizaka
Physical Review B, 16 Aug. 2012
Scientific journal, English

Giant Rashba-type spin splitting in bulk BiTeI
K. Ishizaka; M. S. Bahramy; H. Murakawa; M. Sakano; T. Shimojima; T. Sonobe; K. Koizumi; S. Shin; H. Miyahara; A. Kimura; K. Miyamoto; T. Okuda; H. Namatame; M. Taniguchi; R. Arita; N. Nagaosa; K. Kobayashi; Y. Murakami; R. Kumai; Y. Kaneko; Y. Onose; Y. Tokura
Nature Materials, Jul. 2011
Scientific journal, English

Magnetic properties of vanadium selenide thin films grown by molecular-beam epitaxy II
Nakano Masaki; Yoshida Satoshi; Bahramy Mohammad Saeed; Wang Yue; Matsuoka Hideki; Majima Yuki; Kohama Yoshimitsu; Ohigashi Yuta; Kashiwabara Yuta; Sakano Masato; Ishizaka Kyoko; Iwasa Yoshihiro
The Japan Society of Applied Physics, 2019, JSAP Annual Meetings Extended Abstracts, 66th, 3616-3616, Japanese, 2436-7613, 201902241155533307

Fabrication of atomically thin materials with spin-polarized band structures and exploration of its emergent phenomena
坂野 昌人
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Tokyo, Grant-in-Aid for Scientific Research (B), 24K01285
Apr. 2024 - Mar. 2027

Development of Analysis Methods for 2.5 Dimensional Structures
松田 一成; 末永 和知; 西堀 英治; 坂野 昌人
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Kyoto University, Grant-in-Aid for Transformative Research Areas (A), 学術変革領域（A)「２.５次元物質科学」において、本分析班（A03班）の役割は、２.５次元物質で発現する特異な構造や電子状態の解明に資する分析手法や技術を開発し、その学術の発展を支えることにある。具体的には、本班が供する先端分析技術やそこから明らかとなる学術的知見を通して、集積化を含む物質創製や新奇物性、機能創出によるデバイス応用研究などを支援するとともに、「２.５次元物質科学」の基盤となる分析科学の学理を担う事を目的としている。 昨年度に引き続き、２.５次元物質の研究に資する先端光学などの分析手法の高度化を進めた。特に、二次元物質を積層した際に生じるモアレ構造などの特異な系を対象として、第二高調波発生、極低温発光分光、時間分解分光などの先端光学手法が可能な装置群を広く整備し、領域内外の共同研究に供した。また、X線回折技術として、グラフェンインタカレーションのその場観察実験を開始した。SPring-8の薄膜Ｘ線回折のビームラインで最初の回折実験を行った。その結果を基に、次回以降の実験計画を策定した。加えて、10マイクロメートルサイズのデバイスの構造評価が領域内で重要であることがわかってきたため、その実験を行うための調査を進めた。電子顕微鏡技術および分光技術に関して、可視光領域の吸収スペクトルを角度分解能をもち測定する技術の応用に着手した。それによって、単層グラフェンのギャップやπ励起の分散関係の情報が実験的に得られつつある。角度分解光電子分光を用いたバンド構造の精密測定手法の確立によって、対称性の変化や層間距離の増大に伴う電子構造の変化といった２.５次元物質に特有な物性現象を観測することに成功した。また、電子回折およびX線回折を用いた結晶構造の超高速変化の観測や精密構造評価を行うことによって、電子構造と結晶構造を相補的に分析する技術の開発に取り組んだ。, 21H05235
Sep. 2021 - Mar. 2026

Nontrivial band structure in composite atomic layers studied by micro-focused aser angle-resolved photoelectron spectroscopy
Sakano Masato
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Tokyo, Grant-in-Aid for Scientific Research (B), In this study, we developed a micro-focused laser angle-resolved photoemission spectroscopy system that enables to measure of small (~0.01 mm) samples and a sample fabrication procedure for direct observation of electronic structures in van der Waals heterostructures prepared by a mechanical exfoliation and dry-transfer technique. Using these techniques, we have observed novel electronic structures in transition metal dichalcogenide few-layer materials and twist-stacked materials, which do not appear in bulk crystals, and reveal their origins., 20H01834
Apr. 2020 - Mar. 2023

角度分解光電子分光による極性半導体のスピン軌道相互作用の研究
坂野 昌人
日本学術振興会, 科学研究費助成事業, 東京大学, 特別研究員奨励費, 本年度は、主に下記の3テーマについて、角度分解光電子分光法（ARPES）を用いた強いスピン軌道相互作用と空間反転対称性の破れが創るスピン分裂バンド構造の直接観測と、第一原理バンド計算を基にした微視的機構の解明を目指して、研究を行った。 1.レーザーARPES装置の改良と汎用化 望遠レンズ付きの高感度カメラを用いて2方向から測定試料をリアルタイム観測することによって、~0.1mm程度の試料でも、高精度にフェルミ面の測定を行うことが可能となった。装置性能の評価を行った結果、角度分解能< 0.2度、 偏光度>99%、および測定試料上のレーザーのスポット径~0.1mmを達成した。 2.極性半金属MoTe2におけるトポロジカルバンド構造の研究 MoTe2は低温相において、スピン偏極したアーク状のトポロジカル端状態が存在することが示唆されている。本研究では、自ら開発を進めてきたレーザーARPES装置を用いて、極性を有する結晶構造の表と裏において、異なるトポロジカル端状態が形成されていることを明らかにした。 3.PdBi2における超伝導状態の研究 東大物性研辛研究室と共同研究を行い、低温(~1K)まで到達可能なレーザーARPES装置を用いて、バルクとトポロジカル表面バンドの超伝導状態の電子状態を精査した。転移温度以下において、トポロジカル表面バンド構造においても、フェルミ準位の状態密度が減少し、超伝導ギャップが開く様子が観測された。 本研究課題を通して、当初想定していた極性半導体という範疇を大きく超えて、超伝導体を含む多様な物質において普遍的に存在するスピン軌道相互作用の役割やトポロジカルな性質を明らかにすることに成功した。さらに、所属研究室において1meVを切る高分解能測定が可能なレーザーARPES装置を定常運転化に至らせ、様々な物質の電子構造の高精度・短時間測定を可能にさせた。, 13J09046
Apr. 2013 - Mar. 2016