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Suzuura Hidekatsu

Faculty of Engineering　Applied Physics　Quantum Matter PhysicsProfessor

Researcher basic information

■ Degree
  • 博士（工学）, 東京大学
■ URL
researchmap URLホームページURL■ Various IDs
Researcher number
  • 10282683
ORCID IDResearcher ID
  • F-7605-2012
J-Global ID■ Research Keywords and Fields
Research Keyword
  • カーボンナノチューブ
  • 電子・格子相互作用
  • 電気伝導
  • アンダーソン局在
  • スピン軌道相互作用
  • グラフェン
  • 励起子
  • 低次元電子系
  • 螺旋度
  • 磁気抵抗
  • グラファイト
  • 吸収スペクトル
  • 動的電気伝導率
  • フォノン
  • 発光スペクトル
  • ナノチューブ
  • スピンホール効果
  • 格子不安定性
  • 電気伝度
  • 微細構造分裂
  • 弱局在
  • 光学応答
  • アハラノフ-ボーム効果
  • 熱流体力学
  • 有効質量近似
  • 量子効果
  • 理論
  • 非線形伝導
  • 2次元グラファイト
  • 量子ホール効果
Research Field
  • Natural Science, Semiconductors, optical properties of condensed matter and atomic physics
■ Educational Organization

Career

■ Career
Career
  • May 2025 - Present
    Hokkaido University, Faculty of Engineering Division of Applied Physics, 教授
  • Apr. 2003 - Apr. 2025
    北海道大学 工学(系)研究科(研究院), 准教授

Research activity information

■ Papers
■ Other Activities and Achievements
■ Syllabus
  • 凝縮系物理工学特論, 2024年, 修士課程, 工学院
  • 凝縮系物理工学特論, 2024年, 博士後期課程, 工学院
  • 統計力学Ⅰ, 2024年, 学士課程, 工学部
  • 統計力学Ⅱ, 2024年, 学士課程, 工学部
  • 統計力学演習Ⅰ, 2024年, 学士課程, 工学部
  • 統計力学演習Ⅱ, 2024年, 学士課程, 工学部
■ Research Themes
  • Theoretical study on optical responses of excitons in perovskite solar-cell materials
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    01 Apr. 2020 - 31 Mar. 2024
    鈴浦 秀勝
    今年度は太陽電池ペロブスカイト材料における電子・格子相互作用に起因した励起子吸収スペクトルに対するクーロン相互作用遮蔽効果の理論解析を行った．励起子束縛の強さは電子と正孔のバンド構造から決まる有効質量と実効的な誘電率から定まる．換算質量は電子構造から値を決定できるのに対し，この物質系の誘電率は周波数に強く依存し，静的誘電率は可視光近傍の値と比較して10倍にも及び，束縛エネルギーに換算すれば100分の1となる．実験的にはその中間的な値になることが知られている．単一の周波数を持つアインシュタインフォノンによる電子と正孔の散乱を考慮して光学伝導率を計算することにより，励起子束縛エネルギーに対する動的遮蔽効果の影響を調べた．
    従来の計算ではアインシュタインフォノンによる現実的な誘電率変化では実験で観測される束縛エネルギーの縮小を説明できなかったため，今回は有効モデルとして誘電定数を任意に変化させ影響を調べた．その結果，静的誘電率がいかに大きくなろうとも，現実的なフォノン周波数を考える限り，単一モードのフォノン散乱で達成される遮蔽は不十分であることが明らかになった．静的遮蔽による定数誘電率模型であれば適当な値を設定可能なのに対し，動的効果を取り入れる遮蔽は制限を受けることになる．実際の物質では，極性分子の存在による配向分極が静的遮蔽を支配していると予想され，その方向のランダムネス等の効果を同時に考慮する必要があると考えられる．
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 20K03798
  • Spin current generated by controlling the spatial inversion symmetry in atomic layer structures
    Grants-in-Aid for Scientific Research
    01 Apr. 2017 - 31 Mar. 2021
    Akera Hiroshi
    When the spatial inversion symmetry is globally (or locally) broken in a system, the current through the system generates the global (or local) polarization of the spin angular momentum. Such current-induced spin polarization produces the spin current through an attached electrode. This work has shown that (1) an atomic chain along a helix gives the current-induced spin polarization which is largely modified by controlling the spatial inversion symmetry through the change in the curvature and the torsion of the helix, and that (2) in an atomic layer of group IV element, the current-induced spin polarization changes its direction with changing the electron density.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 17K05484
  • Theoretical study on optical responses of excitons in monolayer transition-metal dichalcogenides
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    01 Apr. 2016 - 31 Mar. 2020
    Suzuura Hidekatsu
    Optical excitation in semiconductors generates electrons and holes and the Coulomb attraction causes formation of the electron-hole bound state what we call exciton. In a monolayer transition-metal dichalcogenide, the exciton plays a dominant role in its optical response because there is no dielectric environment giving rise to screening outside the two-dimensional electronic system. In this study, we have developed a theoretical method to evaluate the dynamical screening effect for excitons. We calculated exciton absorption spectra under several types of dielectric material such as organic solvents and compound semiconductor substrates and discussed the control of optical responses.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 16K05391
  • Theory of nonlinear response induced by electric field in condensed-matter Dirac systems
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    01 Apr. 2013 - 31 Mar. 2016
    SUZUURA Hidekatsu
    Electromagnetic responses in condensed-matter Dirac systems deeply reflect its singular electronic states. We have theoretically studied the enhancement of singular behaviors in optical responses and transport properties due to external electric fields in the Dirac systems. We have shown that external electric fields induce the red shift of strong optical absorption peak due to excitons in carbon nanotubes and that static screening of external electric fields due to edge states in graphene nanoribbons is strongly modulated by electrostatic electron doping. Further, we have also shown that current-induced spatial distributions of spins in topological insulators are highly dependent on the configurations of electrical contacts with external leads.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Principal investigator, Competitive research funding, 25400313
  • Optical Science of Dynamically Correlated Electrons
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    13 Nov. 2008 - 31 Mar. 2014
    GONOKAMI Makoto; AKIYAMA Hidefumi; KANEMITSU Yoshihiko; OGAWA Tetsuo; TANAKA Koichiro; IMOTO Nobuyuki; NOMURA Shintarou; ASHIDA Masaaki; ASANO Kenichi; SUZUURA Hidekatsu; SAKAKI Hiroyuki; TOKURA Yoshinori; KITAGAWA Hiroshi; YUMOTO Jyunji
    As a steering group, we promoted innovative and strong collaborations among four different research groups in quantum optics and spectroscopy, semiconductor device engineering, nanomaterials science, and theoretical physics. We planed and operated a variety of activities such as many symposiums, workshops, meetings, newsletters, and web pages, in order to manage the whole research area cooperatively and actively, encourage young researchers, arrange internal and external evaluations, and send out our research news and messages.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), The University of Tokyo, Coinvestigator not use grants, Competitive research funding, 20104001
  • Dynamical electron correlation and optical response in carbon nanostructures
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    2008 - 2012
    SUZUURA Hidekatsu
    Optical properties of carbon nanotubes and graphene, which are novel low-dimensional material composed of carbon atoms, have theoretically been studied and compared with those of semiconductor-compound quantum structures. In carbon nanotubes, its one-dimensionality strongly enhances the interaction effect so that they have higher potential for external-field control of the optical responses. Absorption coefficient of monolayer graphene is known to have a universal value proportional to the fine-structure constant. This study has clarified that the continuum absorption of band-to-band transitions in semiconductor quantum wells also has the same value.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Hokkaido University, Principal investigator, Competitive research funding, 20104009
  • Theoretical study on quantum transport phenomena originating from unusual electronic states
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    2008 - 2010
    SUZUURA Hidekatsu
    Quantum transport phenomena due to the massless Dirac particles have been studied in semiconductors with spin-orbit interaction and graphene. In the former case, non-zero spin-Hall conductance survives for a finite system with contacts for any impurity density. In the latter, peculiar conduction is given for systems of low impurity density, while Anderson localization takes place for high impurity density as is the case with normal two-dimensional electronic systems.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Principal investigator, Competitive research funding, 20540307
  • カーボンナノチューブにおける電子状態制御と量子輸送現象の理論
    科学研究費助成事業 若手研究(B)
    2005 - 2007
    鈴浦 秀勝
    カーボンナノチューブの不純物散乱に起因する磁気伝導度を強束縛模型に基づき数値的に計算した.常に金属であるアームチェア型と金属と半導体のどちらかの伝導性を示すジグザグ型について調べた結果,金属と半導体で結果を分類できるとした研究計画時の予想とは異なり,アームチェアとジグザグという型による分類が可能であることが明らかになった.
    磁場がチューブ軸と平行な場合,常に金属となるアームチェアナノチューブに対しては磁場を増大することにより伝導率が低下,つまり,正の磁気抵抗が得られた.これは,ゼロ磁場において不純物ポテンシャルによる後方散乱が抑制される機構が破れることによる.対照的に,金属ジグザグナノチューブでは10テスラ程度の強磁場であっても伝導率は増大し,負の磁気抵抗を得る.このチューブの構造に依存した振る舞いは有効質量方程式によれば電子のエネルギー分散の異方性を与える高次の補正項により説明される.その補正項はアームチェア型の場合には先に述べた後方散乱抑制機構に影響を与えないが,ジグザグ型では,小さいながらも,散乱を生む原因となる.軸に平行な磁場はこの補正項を相殺し,散乱を減少させることで負の磁気抵抗を生じる.半導体ジグザグチューブの場合も同様に,エネルギーギャップを生む有効磁束と印加した磁束が相殺することで負の磁気抵抗が実現する.磁場がチューブ軸と直交する時はアームチェア・ジグザグのどちらの場合も伝導率は減少し,正の磁気抵抗が得られた.これはランダウ準位の形成過程で分散が平坦化し,電子の群速度が低下することが原因と考えられる.
    以上の結論から,カーボンナノチューブの磁気伝導はその構造,つまり,電子状態の構造に依存する高次補正項により多彩な振る舞いを示すことが明らかとなり,通常の電子系で期待される普遍的な振る舞いが実験で得られない事実を説明する理論となりうる.
    日本学術振興会, 若手研究(B), 北海道大学, Principal investigator, Competitive research funding, 17740184
  • Thermohydrodynamics in Quantum Hall Systems
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    2004 - 2007
    AKERA Hiroshi; SUZUURA Hidekatsu
    1. A theory of thermohydrodynamics in two-dimensional electron systems in quantizing magnetic fields is developed including a nonlinear transport regime. Spatio-temporal variations of the electron temperature and the chemical potential in the local equilibrium are described by the equations of conservation with the number and thermal-energy flux densities. The theory is applied to calculate spatial variations of these variables in various systems as described in the following.
    2. Spatial distributions of the electron temperature perpendicular to the applied current are obtained in quantum Hall systems with compressible and incompressible strips at low lattice temperatures by solving equations of electron number conservation and energy conservation as well as Poisson's equation self-consistently. In the linear-response regime, variations of the electron temperature concentrate in the incompressible strips as the lattice temperature decreases. The electron temperature indicates an anti-symmetric distribution: it becomes lower than the lattice temperature in the side of a sample with a higher electrochemical potential, and higher in the opposite side. Reflecting the anti-symmetric distribution in the linear-response regime, the current density becomes highly asymmetric as the applied current increases to the breakdown of the quantum Hall effects.
    3. Spatial variations of the electron temperature in the vicinity of metallic current contacts in a quantum Hall system are calculated based on thermohydrodynamics. It is shown that, at larger currents, hot spots with high electron temperatures appear at diagonally opposite corners of the sample. At smaller currents, however, the electron temperature at one of the corners is lower than the lattice temperature, while that at the other is higher than the lattice temperature.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Coinvestigator not use grants, Competitive research funding, 16540278
  • カーボンナノチューブにおける量子輸送現象
    科学研究費助成事業 奨励研究(A)
    2000 - 2001
    鈴浦 秀勝
    カーボンナノチューブの母体となる物質であるグラファイト平面における弱局在効果に関する研究を行った.ナノチューブの場合に習い,谷間散乱を生じる短距相互作用する不純物と,谷内散乱のみを生じる長距離相互作用する不純物という2種類の散乱体を考慮し,久保公式を用いて電気伝導率の計算を解析的に実行した.古典的伝度率に対する量子補正としていわゆる最大交差図形とよばれるダイヤグラムにより表される項を足し合わせた結果,2次元系特有の対数発散する寄与が得られたが,2種類のポテンシャルで符合が異なった.短距離不純物に対しては,系の対称性から予想されるとおり,負の寄与となり通常の弱局在を示す.他方,長距離不純物による散乱では正の寄与となり,反局在を示す.これまで,反局在を示す系はスピン軌道相互作用が散乱に寄与する場合に議論された以外に例が無く非常に興味深い結果である.今後は,対称性による観点からユニバーサリティについて議論しその詳細を明らかにしていくことが必要である.
    前年度に得た電子格子相互作用の有効模型により格子不安定性の議論を行った.電子系の全エネルギーの解析的表式を導き,微小格子変形に対する依存性が強束縛模型から得られる結果と良く一致することを示した.格子不安定性は確かに存在するが,生じる自発的変形は周長に関して指数関数的に減衰するため非常に小さなチューブを除いては実質的に無視できるという,既存の結果と符合する結論となった.しかし,軸に平行な磁場はその不安定性を増大すること,一様な伸縮,ねじれなどが電子と結合しているため外的応力により電子状態を制御可能であることを新たに明らかにした.
    日本学術振興会, 奨励研究(A), 東京大学, Principal investigator, Competitive research funding, 12740173
  • Effects of Magnetic Field on Quantum Phenomena in Carbon Nanotubes
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas (A)
    1999 - 2000
    ANDO Tsuneya; SUZUURA Hidekatsu
    Graphite needles called carbon nanotubes (CN's) were discovered recently and have been a subject of an extensive study. A CN is a few concentric tubes of two-dimensional (2D) graphite consisting of carbon-atom hexagons arranged in a helical fashion about the axis. The distance of adjacent sheets or walls is larger than the distance between nearest neighbor atoms in a graphite sheet and electronic properties are dominated by those of a single layer CN. The purpose of this project is to study effects of magnetic fields on electronic properties of carbon nanotubes theoretically.
    Carbon nanotubes can be either a metal or semiconductor, depending on their diameters and helical arrangement. This condition is obtained based on the band structure of a 2D graphite sheet and periodic boundary conditions along the circumference direction. This result was first predicted by means of a tight-binding model ignoring the effect of the tube curvature and can be well reproduced in a κ・ρ method or an effective-mass approximation. In fact, the effective-mass scheme has been used successfully in the study of wide varieties of electronic properties of CN.
    In this project we have discussed effects of magnetic field on quantum transport of nanotubes based on the κ・ρ method combined with a tight-binding model, such as
    (1) the calculation of the conductance based on analytic treatment of multiple scattering on lattice vacancies in magnetic fields,
    (2) the calculation of the conductance of a junction sytem in magnetic fields and the demonstration on its field-independence,
    (3) the establishment of the long-wavelength phonons in nanotubes and the prediction of a huge positive magnetoresistance at high temperatures, and
    (4) the calculation of scattering phase shift at caps of nantobues and discrete energy levels of capped nanotubes.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas (A), The University of Tokyo, Coinvestigator not use grants, Competitive research funding, 11165211