OMURA Syu

写真a

Affiliation Department etc.

Department of Physical Science and Engineering
Department of Physical Science and Engineering
Center for Innovative Young Researchers

Title

Assistant Professor

 

Papers

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

    Shu Ohmura, Jun Tokimoto, Akira Takahashi

    Physical Review B ( American Physical Society )  104 ( 13 ) 134302   2021.10  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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   2020.07  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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 {φj(t)}. Within
    the framework of MCTDHF, we derived the equations of motion for {φj(t)}. From the derived
    equations, we defined the TD effective potentials veffj(t) that govern the dynamics of φj(t).
    veffj(t) consists of the one-body part v1(t) including the interaction with ε(t) and the two-body
    part v2,j(t) originating from electron–electron interaction. In veff(t) for the 5σ HOMO, a
    narrow hump associated with the increase in v2,5σ(t) is surmounted on the field-distorted
    barrier of v1(t) + v2,5σ(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
    veff(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, veff(t) becomes barrierless,
    enhancing high-harmonic generation through 4σ. We also simulated the dynamics for a
    λ = 380 nm pulse to investigate how veff(t) reflects the nonadiabatic electronic response
    to the pulse. We found that the height of the hump in v1(0) + v2,5σ(t) is nearly proportional
    to the induced dipole moment of φ(t), irrespective of whether the response is adiabatic
    or not. The veffHOMO(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   2020.06  [Refereed]

    Research paper (international conference proceedings)   Multiple Authorship

    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#DjR(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 {veffj(t)} that govern the dynamics of {φ#Dj(t)}. In veff(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 veff(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, veff(t) becomes barrierless, which enhances high-harmonic generation through φ(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     2019.12  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • 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     2019.07  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

Review Papers

  • 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 )    2020.11

    Introduction and explanation (bulletin of university, research institution)   Multiple Authorship

    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.

Presentations

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

    Akira Takahashi, Shu Ohmura

    PIPT7  (Online)  2021.11  -  2021.11  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)  2021.11  -  2021.11  Shuaishuai Sun (Michigan State University)

  • Analysis of strong photoexcitation dynamics in one-dimensional Mott insulators by the time-resolved singular value decomposition

    Shu Ohmura, Jun Tokimoto, Akira Takahashi

    JPS 2021 Autumn Meeting  (Online)  2021.09  -  2021.09  The Physical Society of Japan

  • Coulomb parameter dependence of high harmonic generation in one-dimensional extended Hubbard systems

    Shu Ohmura, Akira Takahashi

    76th Annual Meeting, The Physical Society of Japan  (Online)  2021.03  -  2021.03  The Physical Society of Japan

  • Calculation of the energy eigenstates contributing to the optical conductivity of a two-dimensional Mott insulator using the singular value decomposition

    Satoru Tamakoshi, Jun Tokimoto, Shu Ohmura, Akira Takahashi, Tokitake Yamaguchi, Kaoru Iwano, Hiroshi Okamoto

    76th Annual Meeting, The Physical Society of Japan  (Online)  2021.03  -  2021.03  The Physical Society of Japan

  • Statistical analysis of spin-charge coupled dynamics in a strongly photoexcited one-dimensional Mott insulator

    Takumi Koshino, Shu Ohmura, Akira Takahashi

    JPS 2020 Autumn Meeting  (Online)  2020.09  -  2020.09  The Physical Society of Japan

  • Charge dynamics and high harmonic generation induced by a strong electric field in Mott insulators

    Shu Ohmura, Akira Takahashi

    JPS 2020 Autumn Meeting  (Online)  2020.09  -  2020.09  The Physical Society of Japan

  • Mode analysis of photoexcitation dynamics in a two-dimensional Mott insulator using singular value decomposition

    Satoru Tamakoshi, Shu Ohmura, Akira Takahashi

    JPS 2020 Autumn Meeting  (Online)  2020.09  -  2020.09  The Physical Society of Japan

  • Cluster analysis of the time-dependent wave function in photoexcitation processes of a two-dimensional Mott insulator

    Rikuto Yamachika, Shu Ohmura, Akira Takahashi

    JPS 2020 Autumn Meeting  (Online)  2020.09  -  2020.09  The Physical Society of Japan

  • Dynamics of Terahertz pulse induced transition in dimer Mott insulator κ-(BEDT-TTF)2X

    Takano Yuto, Shu Ohmura, Akira Takahashi

    JPS 2020 Autumn Meeting  (Online)  2020.09  -  2020.09  The Physical Society of Japan

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