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• Ultrafast polarization control in κ-(BEDT-TTF)₂X

  Shu Ohmura, Jun Tokimoto, Akira Takahashi

  Physical Review B ( American Physical Society )  104 ( 13 ) 134302   2021年10月  [査読有り]

  研究論文（学術雑誌）   共著

  We present a theoretical investigation of the dynamics induced by higher-frequency off-resonant light pulse excitation in the metallic phase of κ−(BEDT−TTF)₂X [where BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene and
  X represents a counteranion] by solving the time-dependent Schrödinger equation numerically in the quarter-filled extended Hubbard model for the material. If the magnitude of the applied light pulse exceeds a critical value, the transition to the charge-ordered (CO) state is then induced by the light pulse excitation. In the CO state, one site forming a dimer becomes charge rich, the other site becomes charge poor, and the intradimer electric dipole moments are aligned in a particular direction. The transition is driven by photoinduced reduction of the effective transfer integrals and can therefore be regarded as a dynamical localization-related phenomenon. There are two degenerate A phase and B phase CO states that have opposite polarization directions. The photogenerated CO state is given by the superposition of the A phase and B phase CO states with equal weights, and the polarization of the photogenerated CO state is effectively zero. Transitions to either of the two polarized CO states can be induced selectively, and the polarization can be generated by excitation using light and terahertz pulses. Furthermore, the polarization can be reversed on a timescale of several tens of femtoseconds by excitation using double light and terahertz pulses, which induce the following phase transitions: metal → polarized CO state of the A (B) phase → metal → polarized CO state of the B (A) phase
  → metal.

  

• Analysis of the multielectron dynamics in intense laser-induced ionization of CO by the time-dependent effective potentials for natural orbitals

  Shu Ohmura, Tsuyoshi Kato, Hideki Ohmura, Shiro Koski, Hirohiko Kono

  Journal of Physics B: Atomic, Molecular and Optical Physics ( IOPscience )  53 ( 18 ) 184001   2020年07月  [査読有り]

  研究論文（学術雑誌）   共著

  We simulated the multielectron dynamics of a CO molecule irradiated by near-IR λ = 760 nm
  two-cycle pulses with different carrier envelope phases by using the multiconfiguration
  time-dependent (TD) Hartree–Fock (MCTDHF) method. The ionization rate estimated from
  the simulations is higher when the laser electric field ε(t) points from C to O than in the
  opposite case, in agreement with the results of two-color experiments. The mechanism of the
  directional anisotropy in tunnel ionization of CO was examined by converting the obtained
  multielectron dynamics to the representation in terms of TD natural orbitals {φ_j(t)}. Within
  the framework of MCTDHF, we derived the equations of motion for {φ_j(t)}. From the derived
  equations, we defined the TD effective potentials v^eff_j(t) that govern the dynamics of φ_j(t).
  v^eff_j(t) consists of the one-body part v₁(t) including the interaction with ε(t) and the two-body
  part v_2,j(t) originating from electron–electron interaction. In v^eff_5σ(t) for the 5σ HOMO, a
  narrow hump associated with the increase in v_2,5σ(t) is surmounted on the field-distorted
  barrier of v₁(t) + v_2,5σ(0) near the nucleus C when ε(t) points from C to O, which results in
  the anisotropic ionization of CO. For 4σ, a high barrier that suppresses ionization is formed in
  v^eff_4σ(t) when ε(t) points from C to O, which suggests that dynamical correlation exists between
  4σ and 5σ electrons on route to ionization. For the opposite phase, v^eff_4σ(t) becomes barrierless,
  enhancing high-harmonic generation through 4σ. We also simulated the dynamics for a
  λ = 380 nm pulse to investigate how v^eff_5σ(t) reflects the nonadiabatic electronic response
  to the pulse. We found that the height of the hump in v₁(0) + v_2,5σ(t) is nearly proportional
  to the induced dipole moment of φ_5σ(t), irrespective of whether the response is adiabatic
  or not. The v^eff_HOMO(t) for LiH is also presented to demonstrate the ubiquity of hump structures.

  

• Time-dependent effective potential for the ultrafast correlated electron dynamics of molecules in intense laser fields: Application to anisotropic ionization of CO

  Hirohiko Kono, Shu Ohmura, Tsuyoshi Kato, Hideki Ohmura, Shiro Koseki

  Journal of Physics: Conference Series ( IOPscience )  1412 ( 4 ) 042004   2020年06月  [査読有り]

  研究論文（国際会議プロシーディングス）   共著

  By using the multiconfiguration time-dependent (TD) Hartree-Fock (MCTDHF) method, we simulated the multielectron dynamics of a CO molecule irradiated by near-IR two-cycle pulses with different carrier envelope phases. The ionization rate calculated is higher when the laser electric field ε(t) points from the nucleus C to O than the opposite case, in agreement
  with the results of two-color ionization experiments. The mechanism of anisotropic tunnel ionization in CO was examined by converting the obtained multielectron dynamics to the representation in terms of TD natural orbitals {φ＃Dj_{R(t)}. Within the framework of MCTDHF, we derived the unitary equations of motion for {φj(t)}. From the derived equations, we defined the TD effective potentials {v^effj(t)} that govern the dynamics of {φ#Dj}(t)}. In v^eff_5σ(t) for the 5σ HOMO, a narrow hump that originates from two-body electron-electron repulsion is formed on the top of the field-induced distorted barrier near the nucleus C when ε(t) points from C to O, which is responsible for the directional anisotropy of tunnel ionization. For 4σ HOMO-2, a high
  barrier to suppress ionization is formed in v^eff_4σ(t) when ε(t) points from C to O, in correlation with the electron-electron interaction with a 5σ electron on route to ionization. For the opposite
  phase, v^eff_4σ(t) becomes barrierless, which enhances high-harmonic generation through φ_4σ(t).

  

• A charge model as an effective model of one-dimensional Hubbard and extended Hubbard systems: its application to linear optical spectrum calculations in large systems based upon many-body Wannier functions

  Shu Ohmura, Akira Takahashi, Kaoru Iwano, Tokitake Yamaguchi, Kazuya Shinjo, Takami Tohyama, Shigetoshi Sota, Hiroshi Okamoto

  Physical Review B     2019年12月  [査読有り]

  研究論文（学術雑誌）   共著

• Terahertz pulse induced transitions between ionic and neutral phases and electronic polarization reversal in TTF-CA

  Shu Ohmura, Tomohito Mase, Akira Takahashi

  Physical Review B     2019年07月  [査読有り]

  研究論文（学術雑誌）   共著

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総説・解説記事

• An Effective Model for the One-Dimensional Extended Hubbard Model Applicable to Linear Optical Spectrum Calculations in Large Systems: A New Approach Based on Many-Body Wannier Functions

  Shu Ohmura, Akira Takahashi, Kaoru Iwano, Tokitake Yamaguchi, Kazuya Shinjo, Takami Tohyama, Shigetoshi Sota, Hiroshi Okamoto

  Photon Factory Highlights 2019 ( KEK 高エネルギー加速器研究機構 )    2020年11月

  総説・解説（大学・研究所紀要）   共著

  We have developed a charge model as an effective model of the one-dimensional extended Hubbard model based on
  the spin-charge separation. The charge model includes the effect of charge fluctuations and is applicable to the photoexcitation of one-dimensional Mott insulators. It is numerically shown that the charge model reproduces the optical conductivity spectra calculated by the original model quantitatively. In order to calculate a larger system to compare with experimental results, we also developed a method of many-body Wannier functions (MBWFs). We succeeded in obtaining the optical conductivity spectrum for a large enough system by using the MBWFs constructed from the photoexcited states of the charge model.

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研究発表

• Neutral-ionic phase transitions and ultrafast control of electronic polarization induced by THz pulse in TTF-CA

  Akira Takahashi, Shu Ohmura

  PIPT7  (Online)  2021年11月  -  2021年11月  Shuaishuai Sun (Michigan State University)

• Ultrafast control of polarization in kappa-(BEDT-TTF)₂X by photoinduced phase transition

  Shu Ohmura, Jun Tokimoto, Akira Takahashi

  PIPT7  (Online)  2021年11月  -  2021年11月  Shuaishuai Sun (Michigan State University)

• 一次元中間相関ハバードモデルにおける光励起状態のスピン電荷分離および微小スペクトルピークについて

  時本　純、大村　周、高橋　聡

  日本物理学会2021年秋季大会  (オンライン開催)  2021年09月  -  2021年09月  日本物理学会

• 時間分解特異値分解による1次元モット絶縁体の光強励起ダイナミクスの解析

  大村　周、時本　純、高橋　聡

  日本物理学会2021年秋季大会  (オンライン開催)  2021年09月  -  2021年09月  日本物理学会

• 1次元拡張ハバードモデル系における高次高調波発生のクーロンパラメーター依存性1次元モット絶縁体の光強励起におけるスピン電荷結合の時間分解統計解析

  大村　周、高橋　聡

  第76回年次大会(2021年)  (オンライン開催)  2021年03月  -  2021年03月  日本物理学会

• 二次元モット絶縁体の光学伝導度に寄与するエネルギー固有状態の特異値分解による計算

  玉腰　悟、時本　純、大村　周、高橋　聡、山口　辰威、岩野　薫、岡本　博

  第76回年次大会(2021年)  (オンライン開催)  2021年03月  -  2021年03月  日本物理学会

• 一次元中間相関ハバードモデルにおける光励起状態のRandomized特異値分解による解析

  時本　純、大村　周、越野　巧、佐原　穂紀、高橋　聡

  第76回年次大会(2021年)  (オンライン開催)  2021年03月  -  2021年03月  日本物理学会

• 1次元モット絶縁体における強電場誘起電荷ダイナミクスと高次高調波発生

  大村　周、高橋　聡

  日本物理学会2020年秋季大会  (オンライン開催)  2020年09月  -  2020年09月  日本物理学会

• ダイマーモット絶縁体κ-(BEDT-TTF)₂Xにおけるテラヘルツパルスにより誘起される相転移のダイナミックス

  高野　悠斗、大村　周、高橋　聡

  日本物理学会2020年秋季大会  (オンライン開催)  2020年09月  -  2020年09月  日本物理学会

• 2次元モット絶縁体の光励起過程における時間依存波動関数のクラスター解析

  山近　陸仁、大村　周、高橋　聡

  日本物理学会2020年秋季大会  (オンライン開催)  2020年09月  -  2020年09月  日本物理学会

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