Details of the Researcher

PHOTO

Shunsuke Sato
Section
Graduate School of Science
Job title
Associate Professor
Degree
Researcher ID
I-3294-2015

Research History 9

  • 2025/02 - Present
    Tohoku University　Department of Physics, Faculty of Science　Associate Professor

  • 2019/05 - Present
    Max Planck Institute for the Structure and Dynamics of Matter　Visiting scientist

  • 2024/05 - 2025/01
    University of Tsukuba　Center for Computational Sciences　Associate Professor

  • 2019/05 - 2024/04
    University of Tsukuba　Center for Computational Sciences　Assistant Professor

  • 2017/06 - 2019/05
    Max Planck Institute for the Structure and Dynamics of Matter　Alexander von Humboldt fellow

  • 2017/04 - 2017/05
    Max Planck Institute for the Structure and Dynamics of Matter　Postdoctoral Fellow

  • 2016/04 - 2017/03
    Max Planck Institute for the Structure and Dynamics of Matter　Visiting scientist

  • 2016/04 - 2017/03
    University of Tsukuba　Center for Computational Sciences　Research Fellow (PD) of Japan Society for the Promotion of Science

  • 2014/04 - 2016/03
    University of Tsukuba　Graduate School of Pure and Applied Sciences　Research Fellow (DC1) of Japan Society for the Promotion of Science

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Education 3

  • University of Tsukuba　Graduate School of Pure and Applied Sciences　Doctoral Program in Physics

    2014/04 - 2016/03

  • University of Tsukuba　Graduate School of Pure and Applied Sciences　Master's Program in Physics

    2012/04 - 2014/03

  • University of Tsukuba　School of Science and Engineering　College of Physics

    2008/04 - 2012/03

Research Interests 4

  • Ultrafast phenomena

  • TDDFT

  • First-principles calculation

  • Light-matter interaction

Research Areas 1

  • Natural sciences / Semiconductors, optical and atomic physics /

Awards 2

  1. Condensed-Matter Science Prize

    2024/11

  2. Young Scientist Award of the Physical Society of Japan

    2020/03　Physical Society of Japan

Papers 88

  1. Local fields reveal atomic-scale nonadiabatic carrier-phonon dynamics Peer-reviewed

    Sergej Neb, Dong-bin Shin, Florence Burri, Marko Hollm, Erik W. de Vos, Denis A. Kuznetsov, Christoph R. Müller, Alexey Fedorov, Shunsuke A. Sato, Angel Rubio, Lukas Gallmann, Ursula Keller

    Science　391　(6780)　75-78　2026/01

    Publisher: American Association for the Advancement of Science (AAAS)

    DOI： 10.1126/science.aea1523 　

    ISSN： 0036-8075

    eISSN： 1095-9203

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    Understanding nonadiabatic carrier-lattice interactions at the atomic scale remains a fundamental challenge, yet these processes govern energy transfer in materials and ultimately set limits in microelectronics. We combined attosecond core-level transient absorption spectroscopy with many-body theory to uncover how nonadiabatic electron-phonon coupling drives ultrafast relaxations in a titanium-carbide MXene. Phonon-driven changes in carrier localization modulated local field effects (LFEs), yielding carrier-, site-, and orbital-specific absorption signatures. LFEs served as sensitive fingerprints of electron-phonon coupling strength across the phonon spectrum and revealed a breakdown of the Born–Oppenheimer approximation: Electrons lagged lattice oscillations by 32 ± 8 femtoseconds, whereas holes responded almost instantaneously (7 ± 7 femtoseconds). Our results establish a framework for probing and controlling nonadiabatic carrier-phonon interactions with orbital and site specificity.

  2. Multistate control of nonlinear photocurrents in ferroelectric IV-monochalcogenide monolayers via phase manipulation of the light field Peer-reviewed

    Ali Kazempour, Esmaeil Taghizadeh Sisakht, Mahmut Sait Okyay, Xiao Jiang, Shunsuke Sato, Jinseok Oh, Noejung Park

    Communications Physics　8　(1)　2025/11/17

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s42005-025-02337-1 　

    eISSN： 2399-3650

  3. Technical review: Time-dependent density functional theory for attosecond physics ranging from gas-phase to solids Peer-reviewed

    Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Angel Rubio

    npj Computational Materials　11　(1)　2025/07/15

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41524-025-01715-1 　

    eISSN： 2057-3960

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    Abstract First-principles electron dynamics calculations can be applied in the investigation of a wide range of ultrafast phenomena in attosecond physics. They offer unique microscopic insight into light-induced ultrafast phenomena in both gas and condensed phases of matter, and thus, they are a powerful tool to develop our understanding of the physics of attosecond phenomena. We specifically review techniques employing time-dependent density functional theory (TDDFT) for investigating attosecond and strong-field phenomena. First, we describe this theoretical framework that enables the modeling of perturbative and non-perturbative electron dynamics in materials, including atoms, molecules, and solids. We then discuss its application to attosecond experiments, focusing on the reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) measurements. We also briefly review first-principles calculations of optical properties of solids with TDDFT in the linear response regime and their extension to calculations of transient optical properties of solids in non-equilibrium phases, by simulating experimental pump-probe setups. We further demonstrate the application of TDDFT simulation to high-order harmonic generation in solids. First-principles calculations have predictive power, and hence they can be utilized to design future experiments to explore non-equilibrium and nonlinear ultrafast phenomena in matter and characterize and control metastable light-induced quantum states.

  4. Nonlinear Photocurrent as a Hallmark of Altermagnet Peer-reviewed

    Xiao Jiang, Uiseok Jeong, Shunsuke Sato, Dongbin Shin, Kazuhiro Yabana, Binghai Yan, Noejung Park

    ACS Nano　19　(26)　23620-23628　2025/06/26

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acsnano.5c01421 　

    ISSN： 1936-0851

    eISSN： 1936-086X

  5. Attosecond virtual charge dynamics in dielectrics Peer-reviewed

    Gian Luca Dolso, Shunsuke A. Sato, Giacomo Inzani, Nicola Di Palo, Bruno Moio, Rocío Borrego-Varillas, Mauro Nisoli, Matteo Lucchini

    Nature Photonics　19　(9)　999-1005　2025/06/16

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41566-025-01700-6 　

    ISSN： 1749-4885

    eISSN： 1749-4893

  6. Initial electron thermalization in metals measured by attosecond transient absorption spectroscopy Peer-reviewed

    Bethany R. de Roulet, Lorenz Drescher, Shunsuke A. Sato, Stephen R. Leone

    Physical Review B　110　(17)　2024/11/04

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.110.174301 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  7. Hot electron effect in high-order harmonic generation from graphene driven by elliptically polarized light Peer-reviewed

    Kotaro Nakagawa, Wenwen Mao, Shunsuke A. Sato, Hiroki Ago, Angel Rubio, Yoshihiko Kanemitsu, Hideki Hirori

    APL Photonics　9　(7)　2024/07/01

    Publisher: AIP Publishing

    DOI： 10.1063/5.0212022 　

    eISSN： 2378-0967

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    We studied high-order harmonic generation (HHG) in graphene driven by either linearly or elliptically polarized mid-infrared (MIR) light, and we additionally applied terahertz (THz) pulses to modulate the electron distribution in graphene. The high-harmonic spectrum obtained using linearly polarized MIR light contains only odd-order harmonics. We found that the intensities of the fifth- and seventh-order harmonics are reduced by the modulation with the THz pulses. In addition, we found that the THz-induced reduction of the seventh-order harmonic driven by elliptically polarized MIR light (at ellipticity ε = 0.3) is larger than that of seventh-order harmonic driven by linearly polarized MIR light (ε = 0). The observed behavior can be reproduced by theoretical calculations that consider different electron temperatures (caused by the THz pulses). Furthermore, the observed stronger suppression of HHG driven by elliptically polarized light reveals the following: in the case of elliptically polarized light, the generation of harmonics via interband transitions to conduction-band states that are closer to the Dirac point is more important than in the case of linearly polarized light. In other words, the quantum pathways via interband transitions to low-energy states are the origin of the enhancement of HHG that can be achieved in graphene by using elliptically polarized light.

  8. Nonlinear Current Injection in Hexagonal Boron Nitride using Linearly Polarized Light in a Deeply Off‐Resonant Regime Peer-reviewed

    Wenwen Mao, Angel Rubio, Shunsuke A. Sato

    Advanced Optical Materials　12　(22)　2024/06/21

    Publisher: Wiley

    DOI： 10.1002/adom.202400651 　

    ISSN： 2195-1071

    eISSN： 2195-1071

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    Abstract Light‐induced electron dynamics in monolayer hexagonal boron nitride is theoretically investigated under the influence of two‐color linearly‐polarized laser fields at frequencies ω and 2ω, by solving the time‐dependent Schrödinger equation with a tight‐binding model. In the weak field regime, it is confirm that the injection of ballistic current arises from the breakdown of time‐reversal symmetry. This phenomenon is attributed to quantum interference between two distinct excitation paths: a one‐photon (2ℏω) absorption path and a two‐photon (ℏω) absorption path. In a strong field regime, the analysis reveals that the two‐color laser fields may generate a substantial population imbalance within momentum space, consequently facilitating the injection of ballistic current even in a deeply off‐resonant regime. The findings demonstrate that a pronounced population imbalance exceeding 30% of excited electrons can be realized without relying on the ellipticity of the fields. This highlights the potential of linearly polarized light for efficient photovoltaic effects and valley population control in 2D systems and heterostructures.

  9. Limitations of mean-field approximations in describing shift-current and injection-current in materials Peer-reviewed

    Shunsuke A. Sato, Angel Rubio

    Physical Review B　109　(19)　2024/05/20

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.109.195205 　

    ISSN： 2469-9950

    eISSN： 2469-9969

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    We theoretically and computationally investigate bulk photovoltaic effects, with a specific focus on shift-current and injection-current. Initially, we perform a numerical analysis of the direct current (dc) induced by a laser pulse with a one-dimensional model, utilizing mean-field theories such as time-dependent Hartree–Fock and time-dependent Hartree methods. Our numerical results, obtained with mean-field theories, reveal that the dc component of the current, as a second-order nonlinear effect, exists even after irradiation with linearly polarized light as a second-order nonlinear effect, indicating the generation of injection-current. Conversely, when we employ the independent-particle approximation, no injection-current is generated by linearly polarized light. To develop the microscopic understanding of injection-current within the mean-field approximation, we further analyze the dc component of the current with the perturbation theory, employing the mean-field approximations, the independent-particle approximation, and the exact solution of the many-body Schrödinger equation. The perturbation analysis clarifies that the injection-current induced by linearly polarized light under the mean-field approximations is an artifact caused by population imbalance, created through quantum interference from unphysical self-excitation pathways. Therefore, investigation of many-body effects on the bulk photovoltaic effects have to be carefully conducted in mean-field schemes due to potential contamination by unphysical dc current. Additionally, we perform the first-principles electron dynamics calculation for BaTiO3 based on the time-dependent density functional theory, and we confirm that the above findings from the one-dimensional model calculation and the perturbation analysis apply to realistic systems. Published by the American Physical Society 2024

  10. High-Order Harmonic Generation in Solids: The Role of Intraband Transitions in Extreme Nonlinear Optics Peer-reviewed

    Hideki Hirori, Shunsuke A. Sato, Yoshihiko Kanemitsu

    The Journal of Physical Chemistry Letters　15　(8)　2184-2192　2024/02/19

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.jpclett.3c03415 　

    ISSN： 1948-7185

    eISSN： 1948-7185

  11. Revealing ultrafast phonon mediated inter-valley scattering through transient absorption and high harmonic spectroscopies Peer-reviewed

    Kevin Lively, Shunsuke A. Sato, Guillermo Albareda, Angel Rubio, Aaron Kelly

    Physical Review Research　6　(1)　2024/01/19

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevresearch.6.013069 　

    eISSN： 2643-1564

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    Processes involving ultrafast laser driven electron-phonon dynamics play a fundamental role in the response of quantum systems in a growing number of situations of interest, as evinced by phenomena such as strongly driven phase transitions and light driven engineering of material properties. To show how these processes can be captured from a computational perspective, we simulate the transient absorption spectra and high-harmonic generation signals associated with valley selective excitation and intraband charge-carrier relaxation in monolayer hexagonal boron nitride. We show that the multitrajectory Ehrenfest dynamics approach, implemented in combination with real-time time-dependent density-functional theory and tight-binding models, offers a simple, accurate, and efficient method to study ultrafast electron-phonon coupled phenomena in solids under diverse pump-probe regimes which can be easily incorporated into the majority of real-time software packages. Published by the American Physical Society 2024

  12. Enhancement of high-order harmonic generation in graphene by mid-infrared and terahertz fields Peer-reviewed

    Wenwen Mao, Angel Rubio, Shunsuke A. Sato

    Physical Review B　109　(4)　2024/01/17

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.109.045421 　

    ISSN： 2469-9950

    eISSN： 2469-9969

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    We theoretically investigate high-order harmonic generation (HHG) in graphene under mid-infrared (MIR) and terahertz (THz) fields based on a quantum master equation. Numerical simulations show that MIR-induced HHG in graphene can be enhanced by a factor of 10 for fifth harmonic and a factor of 25 for seventh harmonic under a THz field with a peak strength of 0.5 MV/cm by optimizing the relative angle between the MIR and THz fields. To identify the origin of this enhancement, we compare the fully dynamical calculations with a simple thermodynamic model and a nonequilibrium population model. The analysis shows that the enhancement of the high-order harmonics mainly results from a coherent coupling between MIR- and THz-induced transitions that goes beyond a simple THz-induced population contribution. Published by the American Physical Society 2024

  13. Enhancing high harmonic generation in GaAs by elliptically polarized light excitation Peer-reviewed

    Fumiya Sekiguchi, Minoru Sakamoto, Kotaro Nakagawa, Hirokazu Tahara, Shunsuke A. Sato, Hideki Hirori, Yoshihiko Kanemitsu

    Physical Review B　108　(20)　2023/11/13

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.108.205201 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  14. Frequency-resolved Microscopic Current Density Analysis of Linear and Nonlinear Optical Phenomena in Solids Peer-reviewed

    Shunsuke A. Sato

    Journal of the Physical Society of Japan　92　(9)　2023/09/15

    Publisher: Physical Society of Japan

    DOI： 10.7566/jpsj.92.094401 　

    ISSN： 0031-9015

    eISSN： 1347-4073

  15. Optimizing Floquet engineering for non-equilibrium steady states with gradient-based methods Peer-reviewed

    Alberto Castro, Shunsuke Sato

    SciPost Physics　15　(1)　2023/07/26

    Publisher: Stichting SciPost

    DOI： 10.21468/scipostphys.15.1.029 　

    eISSN： 2542-4653

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    Non-equilibrium steady states are created when a periodically driven quantum system is also incoherently interacting with an environment - as it is the case in most realistic situations. The notion of Floquet engineering refers to the manipulation of the properties of systems under periodic perturbations. Although it more frequently refers to the coherent states of isolated systems (or to the transient phase for states that are weakly coupled to the environment), it may sometimes be of more interest to consider the final steady states that are reached after decoherence and dissipation take place. In this work, we demonstrate how those final states can be optimally tuned with respect to a given predefined metric, such as for example the maximization of the temporal average value of some observable, by using multicolor periodic perturbations. We show a computational framework that can be used for that purpose, and exemplify the concept using a simple model for the nitrogen-vacancy center in diamond: the goal in this case is to find the driving periodic magnetic field that maximizes a time-averaged spin component. We show that, for example, this technique permits to prepare states whose spin values are forbidden in thermal equilibrium at any temperature.

  16. Gapless detection of broadband terahertz pulses using a metal surface in air based on field-induced second-harmonic generation Peer-reviewed

    Shunsuke Tanaka, Yuta Murotani, Shunsuke A. Sato, Tomohiro Fujimoto, Takuya Matsuda, Natsuki Kanda, Ryusuke Matsunaga, Jun Yoshinobu

    Applied Physics Letters　122　(25)　2023/06/19

    Publisher: AIP Publishing

    DOI： 10.1063/5.0153667 　

    ISSN： 0003-6951

    eISSN： 1077-3118

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    We investigate second-harmonic generation (SHG) light from a Pt surface in atmosphere under terahertz (THz) pulses. THz pulse-modulated SHG intensity,  ΔI2ω, shows a clear time profile of the THz field, which is similar to that of the conventional electro-optic sampling. The result can be explained by interference between THz field-induced second-harmonic light from air molecules in an optical path and a local oscillator from a Pt surface, whereby heterodyne detection of the THz waveform can be achieved. Using numerical calculations of a wave equation, we discuss the contribution of the Gouy phases of all the pulses, including near-infrared, SHG, and THz pulses, and identification of effective nonlinear susceptibility of the Pt surface. Our method, simply using a polished metal surface and air molecules, does not suffer from phonons or phase matching in solid-state optics and does not require any power supply, bias voltage, or fabrication process, but it offers a simple and gapless sampling method for broadband THz pulses. Here, we demonstrate the gapless detection of a broadband THz pulse in the region of 0.2–20 THz using this method.

  17. Floquet-Bloch resonances in near-petahertz electroabsorption spectroscopy of SiO2 Peer-reviewed

    M. Volkov, S. A. Sato, A. Niedermayr, A. Rubio, L. Gallmann, U. Keller

    Physical Review B　107　(18)　2023/05/05

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.107.184304 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  18. Ultrafast electron localization and screening in a transition metal dichalcogenide Peer-reviewed

    Z. Schumacher, S. A. Sato, S. Neb, A. Niedermayr, L. Gallmann, A. Rubio, U. Keller

    Proceedings of the National Academy of Sciences　120　(15)　2023/04/04

    Publisher: Proceedings of the National Academy of Sciences

    DOI： 10.1073/pnas.2221725120 　

    ISSN： 0027-8424

    eISSN： 1091-6490

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    The coupling of light to electrical charge carriers in semiconductors is the foundation of many technological applications. Attosecond transient absorption spectroscopy measures simultaneously how excited electrons and the vacancies they leave behind dynamically react to the applied optical fields. In compound semiconductors, these dynamics can be probed via any of their atomic constituents with core-level transitions into valence and conduction band. Typically, the atomic species forming the compound contribute comparably to the relevant electronic properties of the material. One therefore expects to observe similar dynamics, irrespective of the choice of atomic species via which it is probed. Here, we show in the two-dimensional transition metal dichalcogenide semiconductor MoSe 2 , that through a selenium-based core-level transition we observe charge carriers acting independently from each other, while when probed through molybdenum, the collective, many-body motion of the carriers dominates. Such unexpectedly contrasting behavior can be explained by a strong localization of electrons around molybdenum atoms following absorption of light, which modifies the local fields acting on the carriers. We show that similar behavior in elemental titanium metal [M. Volkov et al. , Nat. Phys. 15 , 1145–1149 (2019)] carries over to transition metal-containing compounds and is expected to play an essential role for a wide range of such materials. Knowledge of independent particle and collective response is essential for fully understanding these materials.

  19. Floquet band engineering in action Peer-reviewed

    Hannes Hübener, Umberto De Giovannini, Shunsuke A. Sato, Angel Rubio

    Science Bulletin　68　(8)　751-752　2023/04

    Publisher: Elsevier BV

    DOI： 10.1016/j.scib.2023.03.046 　

    ISSN： 2095-9273

  20. Floquet engineering with quantum optimal control theory Peer-reviewed

    Alberto Castro, Umberto De Giovannini, Shunsuke A Sato, Hannes Hübener, Angel Rubio

    New Journal of Physics　25　(4)　043023-043023　2023/04/01

    Publisher: IOP Publishing

    DOI： 10.1088/1367-2630/accb05 　

    eISSN： 1367-2630

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    Abstract Floquet engineering consists in the modification of physical systems by the application of periodic time-dependent perturbations. The search for the shape of the periodic perturbation that best modifies the properties of a system in order to achieve some predefined metastable target behavior can be formulated as an optimal control problem. We discuss several ways to formulate and solve this problem. We present, as examples, some applications in the context of material science, although the methods discussed here are valid for any quantum system (from molecules and nanostructures to extended periodic and non periodic quantum materials). In particular, we show how one can achieve the manipulation of the Floquet pseudo-bandstructure of a transition metal dichalcogenide monolayer (MoS2).

  21. Second harmonic Hall responses of insulators as a probe of Berry curvature dipole Peer-reviewed

    Mahmut Sait Okyay, Shunsuke A. Sato, Kun Woo Kim, Binghai Yan, Hosub Jin, Noejung Park

    Communications Physics　5　(1)　2022/11/26

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s42005-022-01086-9 　

    eISSN： 2399-3650

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    Abstract Diverse nonlinear optical responses of metallic band states have been characterized in terms of the Berry curvature dipole (BCD) or other multipole structures of Berry curvature. Here, we find that the second harmonic optical responses of insulators to sub-bandgap light are also delicately associated with the interband BCD. We performed real-time time-dependent density functional theory calculations and theoretically analyzed the second harmonic generation susceptibility tensors. The two-band term of the second-order susceptibility is precisely proportional to the interband BCD, which is particularly significant for low-symmetric systems with a small bandgap. We show that higher-order responses to nonperturbative strong fields can be associated with higher poles of Berry curvature. We suggest that the consequences of symmetry lowering can be detected by nonlinear optical responses through adjustments of the dipole or other multipole structures of the Berry curvature texture.

  22. Controlling Floquet states on ultrashort time scales Peer-reviewed

    Matteo Lucchini, Fabio Medeghini, Yingxuan Wu, Federico Vismarra, Rocío Borrego-Varillas, Aurora Crego, Fabio Frassetto, Luca Poletto, Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Ángel Rubio, Mauro Nisoli

    Nature Communications　13　(1)　2022/11/19

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41467-022-34973-4 　

    eISSN： 2041-1723

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    Abstract The advent of ultrafast laser science offers the unique opportunity to combine Floquet engineering with extreme time resolution, further pushing the optical control of matter into the petahertz domain. However, what is the shortest driving pulse for which Floquet states can be realised remains an unsolved matter, thus limiting the application of Floquet theory to pulses composed by many optical cycles. Here we ionized Ne atoms with few-femtosecond pulses of selected time duration and show that a Floquet state can be observed already with a driving field that lasts for only 10 cycles. For shorter pulses, down to 2 cycles, the finite lifetime of the driven state can still be explained using an analytical model based on Floquet theory. By demonstrating that the amplitude and number of Floquet-like sidebands in the photoelectron spectrum can be controlled not only with the driving laser pulse intensity and frequency, but also by its duration, our results add a new lever to the toolbox of Floquet engineering.

  23. Simulating Terahertz Field-Induced Ferroelectricity in Quantum Paraelectric SrTiO3 Peer-reviewed

    Dongbin Shin, Simone Latini, Christian Schäfer, Shunsuke A. Sato, Edoardo Baldini, Umberto De Giovannini, Hannes Hübener, Angel Rubio

    Physical Review Letters　129　(16)　2022/10/10

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevlett.129.167401 　

    ISSN： 0031-9007

    eISSN： 1079-7114

  24. Charge transfer in ultrafast isomerization of acetylene ions Peer-reviewed

    Wan-Dong Yu, Hao Liang, Cong-Zhang Gao, Shunsuke A. Sato, Bao-Ren Wei, Alberto Castro, Angel Rubio, Liang-You Peng

    Physical Review A　106　(3)　2022/09/20

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.106.033111 　

    ISSN： 2469-9926

    eISSN： 2469-9934

  25. Floquet engineering the band structure of materials with optimal control theory Peer-reviewed

    Alberto Castro, Umberto De Giovannini, Shunsuke A. Sato, Hannes Hübener, Angel Rubio

    Physical Review Research　4　(3)　2022/09/19

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevresearch.4.033213 　

    eISSN： 2643-1564

  26. Time- and angle-resolved photoelectron spectroscopy of strong-field light-dressed solids: Prevalence of the adiabatic band picture Peer-reviewed

    Ofer Neufeld, Wenwen Mao, Hannes Hübener, Nicolas Tancogne-Dejean, Shunsuke A. Sato, Umberto De Giovannini, Angel Rubio

    Physical Review Research　4　(3)　2022/08/04

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevresearch.4.033101 　

    eISSN： 2643-1564

  27. Terahertz-induced high-order harmonic generation and nonlinear charge transport in graphene Peer-reviewed

    Wenwen Mao, Angel Rubio, Shunsuke A. Sato

    Physical Review B　106　(2)　2022/07/29

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.106.024313 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  28. Size-controlled quantum dots reveal the impact of intraband transitions on high-order harmonic generation in solids Peer-reviewed

    Kotaro Nakagawa, Hideki Hirori, Shunsuke A. Sato, Hirokazu Tahara, Fumiya Sekiguchi, Go Yumoto, Masaki Saruyama, Ryota Sato, Toshiharu Teranishi, Yoshihiko Kanemitsu

    Nature Physics　18　(8)　874-878　2022/06/23

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41567-022-01639-3 　

    ISSN： 1745-2473

    eISSN： 1745-2481

  29. Few-Femtosecond Dynamics of Free-Free Opacity in Optically Heated Metals Peer-reviewed

    A. Niedermayr, M. Volkov, S. A. Sato, N. Hartmann, Z. Schumacher, S. Neb, A. Rubio, L. Gallmann, U. Keller

    Physical Review X　12　(2)　2022/05/25

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevx.12.021045 　

    eISSN： 2160-3308

  30. Reconstruction of ultrafast exciton dynamics with a phase-retrieval algorithm Peer-reviewed

    Gian Luca Dolso, Bruno Moio, Giacomo Inzani, Nicola Di Palo, Shunsuke A. Sato, Rocío Borrego-Varillas, Mauro Nisoli, Matteo Lucchini

    Optics Express　30　(8)　12248-12248　2022/03/28

    Publisher: Optica Publishing Group

    DOI： 10.1364/oe.451759 　

    eISSN： 1094-4087

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    The first step to gain optical control over the ultrafast processes initiated by light in solids is a correct identification of the physical mechanisms at play. Among them, exciton formation has been identified as a crucial phenomenon which deeply affects the electro-optical properties of most semiconductors and insulators of technological interest. While recent experiments based on attosecond spectroscopy techniques have demonstrated the possibility to observe the early-stage exciton dynamics, the description of the underlying exciton properties remains non-trivial. In this work we propose a new method called extended Ptychographic Iterative engine for eXcitons (ePIX), capable of reconstructing the main physical properties which determine the evolution of the quasi-particle with no prior knowledge of the exact relaxation dynamics or the pump temporal characteristics. By demonstrating its accuracy even when the exciton dynamics is comparable to the pump pulse duration, ePIX is established as a powerful approach to widen our knowledge of solid-state physics.

  31. First-principles calculations for transient absorption of laser-excited magnetic materials Peer-reviewed

    Shunsuke A Sato

    Electronic Structure　4　(1)　014007-014007　2022/02/28

    Publisher: IOP Publishing

    DOI： 10.1088/2516-1075/ac52df 　

    eISSN： 2516-1075

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    Abstract We investigate the modification in the optical properties of laser-excited bulk cobalt and nickel using the time-dependent density functional theory at a finite electron temperature. As a result of the first-principles simulation, a complex change in the photoabsorption of the magnetic materials is observed around the M 2,3 absorption edge. Based on the microscopic analysis, we clarify that this complex absorption change consists of the two following components: (i) the decrease in the photoabsorption in a narrow energy range around the M 2,3 edge, which reflects the blue shift of the absorption edge due to the light-induced demagnetization, and (ii) the increase in the photoabsorption in a wider range around the M 2,3 edge, which reflects the modification in the local-field effect due to the light-induced electron localization. The relation between the transient optical and magnetic properties may open a way to monitor ultrafast (de)magnetization and spin dynamics in magnetic materials via transient absorption spectroscopy.

  32. First-principles modelling for time-resolved ARPES under different pump–probe conditions Peer-reviewed

    Umberto De Giovannini, Shunsuke A. Sato, Hannes Hübener, Angel Rubio

    Journal of Electron Spectroscopy and Related Phenomena　254　147152-147152　2022/01

    Publisher: Elsevier BV

    DOI： 10.1016/j.elspec.2021.147152 　

    ISSN： 0368-2048

  33. Two-step Brillouin zone sampling for efficient computation of electron dynamics in solids Peer-reviewed

    Shunsuke A Sato

    Journal of Physics: Condensed Matter　34　(9)　095903-095903　2021/12/16

    Publisher: IOP Publishing

    DOI： 10.1088/1361-648x/ac3f00 　

    ISSN： 0953-8984

    eISSN： 1361-648X

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    Abstract We develop a numerical Brillouin-zone integration scheme for real-time propagation of electronic systems with time-dependent density functional theory. This scheme is based on the decomposition of a large simulation into a set of small independent simulations. The performance of the decomposition scheme is examined in both linear and nonlinear regimes by computing the linear optical properties of bulk silicon and high-order harmonic generation. The decomposition of a large simulation into a set of independent simulations can improve the efficiency of parallel computation by reducing communication and synchronization overhead and enhancing the portability of simulations across a relatively small cluster machine.

  34. Conditional Wave Function Theory: A Unified Treatment of Molecular Structure and Nonadiabatic Dynamics Peer-reviewed

    Guillermo Albareda, Kevin Lively, Shunsuke A. Sato, Aaron Kelly, Angel Rubio

    Journal of Chemical Theory and Computation　17　(12)　7321-7340　2021/11/09

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.jctc.1c00772 　

    ISSN： 1549-9618

    eISSN： 1549-9626

  35. Quantum paraelectric phase of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>SrTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> from first principles Peer-reviewed

    Dongbin Shin, Simone Latini, Christian Schäfer, Shunsuke A. Sato, Umberto De Giovannini, Hannes Hübener, Angel Rubio

    Physical Review B　104　(6)　2021/08/10

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.104.l060103 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  36. The ferroelectric photo ground state of SrTiO 3 : Cavity materials engineering Peer-reviewed

    Simone Latini, Dongbin Shin, Shunsuke A. Sato, Christian Schäfer, Umberto De Giovannini, Hannes Hübener, Angel Rubio

    Proceedings of the National Academy of Sciences　118　(31)　2021/07/27

    Publisher: Proceedings of the National Academy of Sciences

    DOI： 10.1073/pnas.2105618118 　

    ISSN： 0027-8424

    eISSN： 1091-6490

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    Significance Controlling collective phenomena in quantum materials is a promising route toward engineering material properties on demand. Strong THz lasers have been successful at inducing ferroelectricity in . Here we demonstrate, from atomistic calculations, that cavity quantum vacuum fluctuations induce a change in the collective phase of in the strong light–matter coupling regime. Under these conditions, the ferroelectric phase is stabilized as the ground state, instead of the quantum paraelectric one. We conceptualize this light–matter hybrid state as a material photo ground state: Fundamental properties such as crystal structure, phonon frequencies, and the collective phase of a material are determined by the quantum light–matter coupling in equilibrium conditions. Cavity-coupling adds a new dimension to the phase diagram of .

  37. Survival of Floquet–Bloch States in the Presence of Scattering Peer-reviewed

    Sven Aeschlimann, Shunsuke A. Sato, Razvan Krause, Mariana Chávez-Cervantes, Umberto De Giovannini, Hannes Hübener, Stiven Forti, Camilla Coletti, Kerstin Hanff, Kai Rossnagel, Angel Rubio, Isabella Gierz

    Nano Letters　21　(12)　5028-5035　2021/06/04

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.nanolett.1c00801 　

    ISSN： 1530-6984

    eISSN： 1530-6992

  38. Nonlinear electric conductivity and THz-induced charge transport in graphene Peer-reviewed

    Shunsuke A Sato, Angel Rubio

    New Journal of Physics　23　(6)　063047-063047　2021/06/01

    Publisher: IOP Publishing

    DOI： 10.1088/1367-2630/ac03d0 　

    eISSN： 1367-2630

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    Abstract Based on the quantum master equation approach, the nonlinear electric conductivity of graphene is investigated under static electric fields for various chemical potential shifts. The simulation results show that, as the field strength increases, the effective conductivity is firstly suppressed, reflecting the depletion of effective carriers due to the large displacement in the Brillouin zone caused by the strong field. Then, as the field strength exceeds 1 MV m−1, the effective conductivity increases, overcoming the carrier depletion via the Landau–Zener tunneling process. Based on the nonlinear behavior of the conductivity, the charge transport induced by few-cycle THz pulses is studied to elucidate the ultrafast control of electric current in matter.

  39. First-principles calculations for attosecond electron dynamics in solids Peer-reviewed

    Shunsuke A. Sato

    Computational Materials Science　194　110274-110274　2021/06

    Publisher: Elsevier BV

    DOI： 10.1016/j.commatsci.2020.110274 　

    ISSN： 0927-0256

  40. Simulating Vibronic Spectra without Born–Oppenheimer Surfaces Peer-reviewed

    Kevin Lively, Guillermo Albareda, Shunsuke A. Sato, Aaron Kelly, Angel Rubio

    The Journal of Physical Chemistry Letters　12　(12)　3074-3081　2021/03/22

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.jpclett.1c00073 　

    ISSN： 1948-7185

    eISSN： 1948-7185

  41. Single and double charge transfer in the Ne2++He collision within time-dependent density-functional theory Peer-reviewed

    Wandong Yu, Cong-Zhang Gao, Shunsuke A. Sato, Alberto Castro, Angel Rubio, Baoren Wei

    Physical Review A　103　(3)　2021/03/12

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.103.032816 　

    ISSN： 2469-9926

    eISSN： 2469-9934

  42. Unravelling the intertwined atomic and bulk nature of localised excitons by attosecond spectroscopy Peer-reviewed

    Matteo Lucchini, Shunsuke A. Sato, Giacinto D. Lucarelli, Bruno Moio, Giacomo Inzani, Rocío Borrego-Varillas, Fabio Frassetto, Luca Poletto, Hannes Hübener, Umberto De Giovannini, Angel Rubio, Mauro Nisoli

    Nature Communications　12　(1)　2021/02/15

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41467-021-21345-7 　

    eISSN： 2041-1723

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    Abstract The electro-optical properties of most semiconductors and insulators of technological interest are dominated by the presence of electron-hole quasi-particles, called excitons. The manipulation of excitons in dielectrics has recently received great attention, with possible applications in different fields including optoelectronics and photonics. Here, we apply attosecond transient reflection spectroscopy in a sequential two-foci geometry and observe sub-femtosecond dynamics of a core-level exciton in bulk MgF2 single crystals. Furthermore, we access absolute phase delays, which allow for an unambiguous comparison with theoretical calculations. Our results show that excitons surprisingly exhibit a dual atomic- and solid-like character, which manifests itself on different time scales. While the former is responsible for a femtosecond optical Stark effect, the latter dominates the attosecond excitonic response. Further theoretical investigation reveals a link with the exciton sub-femtosecond nanometric motion and allows us to envision a new route to control exciton dynamics in the close-to-petahertz regime.

  43. High-order harmonic generation in graphene: Nonlinear coupling of intraband and interband transitions Peer-reviewed

    Shunsuke A. Sato, Hideki Hirori, Yasuyuki Sanari, Yoshihiko Kanemitsu, Angel Rubio

    Physical Review B　103　(4)　2021/01/29

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.103.l041408 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  44. Floquet dynamics in light-driven solids Peer-reviewed

    M. Nuske, L. Broers, B. Schulte, G. Jotzu, S. A. Sato, A. Cavalleri, A. Rubio, J. W. McIver, L. Mathey

    Physical Review Research　2　(4)　2020/12/22

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevresearch.2.043408 　

    eISSN： 2643-1564

  45. Dynamical amplification of electric polarization through nonlinear phononics in 2D SnTe Peer-reviewed

    Dongbin Shin, Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Noejung Park, Angel Rubio

    npj Computational Materials　6　(1)　2020/11/30

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41524-020-00449-6 　

    eISSN： 2057-3960

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    Abstract Ultrafast optical control of ferroelectricity using intense terahertz fields has attracted significant interest. Here we show that the nonlinear interactions between two optical phonons in SnTe, a two-dimensional in-plane ferroelectric material, enables a dynamical amplification of the electric polarization within subpicoseconds time domain. Our first-principles time-dependent simulations show that the infrared-active out-of-plane phonon mode, pumped to nonlinear regimes, spontaneously generates in-plane motions, leading to rectified oscillations in the in-plane electric polarization. We suggest that this dynamical control of ferroelectric material, by nonlinear phonon excitation, can be utilized to achieve ultrafast control of the photovoltaic or other nonlinear optical responses.

  46. Floquet states in dissipative open quantum systems Peer-reviewed

    S A Sato, U De Giovannini, S Aeschlimann, I Gierz, H Hübener, A Rubio

    Journal of Physics B: Atomic, Molecular and Optical Physics　53　(22)　225601-225601　2020/10/22

    Publisher: IOP Publishing

    DOI： 10.1088/1361-6455/abb127 　

    ISSN： 0953-4075

    eISSN： 1361-6455

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    Abstract We theoretically investigate basic properties of nonequilibrium steady states of periodically-driven open quantum systems based on the full solution of the Maxwell–Bloch equation. In a resonant driving condition, we find that the transverse relaxation, also known as decoherence, significantly destructs the formation of Floquet states while the longitudinal relaxation does not directly affect it. Furthermore, by evaluating the quasienergy spectrum of the nonequilibrium steady states, we demonstrate that Rabi splitting can be observed as long as the decoherence time is as short as one third of the Rabi-cycle. Moreover, we find that Floquet states can be formed even under significant dissipation when the decoherence time is substantially shorter than the cycle of driving, once the driving field strength becomes strong enough. In an off-resonant condition, we demonstrate that the Floquet states can be realized even in weak field regimes because the system is not excited and the decoherence mechanism is not activated. Once the field strength becomes strong enough, the system can be excited by multi-photon absorption and the decoherence process becomes active. As a result, the Floquet states are significantly disturbed by the environment even in the off-resonant condition. Thus, we show here that the suppression of energy transfer from light to matter is a key condition for the realization of Floquet states in both on- and off-resonant conditions not only because it prevents material damage but also because it contributes to preserving coherence.

  47. Direct Measurement of Electron-Phonon Coupling with Time-Resolved ARPES Peer-reviewed

    Umberto De Giovannini, Hannes Hübener, Shunsuke A. Sato, Angel Rubio

    Physical Review Letters　125　(13)　2020/09/21

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevlett.125.136401 　

    ISSN： 0031-9007

    eISSN： 1079-7114

  48. Role of electron scattering on the high-order harmonic generation from solids Peer-reviewed

    Chang-Ming Wang, Nicolas Tancogne-Dejean, Massimo Altarelli, Angel Rubio, Shunsuke A. Sato

    Physical Review Research　2　(3)　2020/08/28

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevresearch.2.033333 　

    eISSN： 2643-1564

  49. Role of virtual band population for high harmonic generation in solids Peer-reviewed

    Yasuyuki Sanari, Hideki Hirori, Tomoko Aharen, Hirokazu Tahara, Yasushi Shinohara, Kenichi L. Ishikawa, Tomohito Otobe, Peiyu Xia, Nobuhisa Ishii, Jiro Itatani, Shunsuke A. Sato, Yoshihiko Kanemitsu

    Physical Review B　102　(4)　2020/07/30

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.102.041125 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  50. Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides Peer-reviewed

    Jiaojian Shi, Edoardo Baldini, Simone Latini, Shunsuke A. Sato, Yaqing Zhang, Brandt C. Pein, Pin-Chun Shen, Jing Kong, Angel Rubio, Nuh Gedik, Keith A. Nelson

    Nano Letters　20　(7)　5214-5220　2020/06/15

    Publisher: American Chemical Society (ACS)

    DOI： 10.1021/acs.nanolett.0c01134 　

    ISSN： 1530-6984

    eISSN： 1530-6992

  51. Octopus, a computational framework for exploring light-driven phenomena and quantum dynamics in extended and finite systems Peer-reviewed

    Nicolas Tancogne-Dejean, Micael J. T. Oliveira, Xavier Andrade, Heiko Appel, Carlos H. Borca, Guillaume Le Breton, Florian Buchholz, Alberto Castro, Stefano Corni, Alfredo A. Correa, Umberto De Giovannini, Alain Delgado, Florian G. Eich, Johannes Flick, Gabriel Gil, Adrián Gomez, Nicole Helbig, Hannes Hübener, René Jestädt, Joaquim Jornet-Somoza, Ask H. Larsen, Irina V. Lebedeva, Martin Lüders, Miguel A. L. Marques, Sebastian T. Ohlmann, Silvio Pipolo, Markus Rampp, Carlo A. Rozzi, David A. Strubbe, Shunsuke A. Sato, Christian Schäfer, Iris Theophilou, Alicia Welden, Angel Rubio

    The Journal of Chemical Physics　152　(12)　2020/03/31

    Publisher: AIP Publishing

    DOI： 10.1063/1.5142502 　

    ISSN： 0021-9606

    eISSN： 1089-7690

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    Over the last few years, extraordinary advances in experimental and theoretical tools have allowed us to monitor and control matter at short time and atomic scales with a high degree of precision. An appealing and challenging route toward engineering materials with tailored properties is to find ways to design or selectively manipulate materials, especially at the quantum level. To this end, having a state-of-the-art ab initio computer simulation tool that enables a reliable and accurate simulation of light-induced changes in the physical and chemical properties of complex systems is of utmost importance. The first principles real-space-based Octopus project was born with that idea in mind, i.e., to provide a unique framework that allows us to describe non-equilibrium phenomena in molecular complexes, low dimensional materials, and extended systems by accounting for electronic, ionic, and photon quantum mechanical effects within a generalized time-dependent density functional theory. This article aims to present the new features that have been implemented over the last few years, including technical developments related to performance and massive parallelism. We also describe the major theoretical developments to address ultrafast light-driven processes, such as the new theoretical framework of quantum electrodynamics density-functional formalism for the description of novel light–matter hybrid states. Those advances, and others being released soon as part of the Octopus package, will allow the scientific community to simulate and characterize spatial and time-resolved spectroscopies, ultrafast phenomena in molecules and materials, and new emergent states of matter (quantum electrodynamical-materials).

  52. Attosecond timing of the dynamical Franz–Keldysh effect Peer-reviewed

    M Lucchini, S A Sato, F Schlaepfer, K Yabana, L Gallmann, A Rubio, U Keller

    Journal of Physics: Photonics　2　(2)　025001-025001　2020/02/18

    Publisher: IOP Publishing

    DOI： 10.1088/2515-7647/ab70cb 　

    eISSN： 2515-7647

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    Abstract To what extent do intra- or inter-band transitions dominate the optical response of dielectrics when pumped by a few-cycle near-infrared transient electric field? In order to find an answer to this question we investigate the dynamical Franz–Keldysh effect in polycrystalline diamond and discuss in detail the attosecond delay of the induced electron dynamics with regard to the driving transient electric field while the peak intensity is varied between 1 × 1012 and 10 × 1012 W cm−2. We found that the main oscillating feature in transient absorption at 43 eV is in phase with the electric field of the pump, to within 49 ± 78 as. However, the phase delay shows a slightly asymmetric V-shaped linear energy dispersion with a rate of about 200 as eV–1. Theoretical calculations within the dipole approximation reproduce the data and allow us to conclude that intra-band motion dominates under our experimental conditions.

  53. Exact exchange-correlation potential of effectively interacting Kohn-Sham systems Peer-reviewed

    Shunsuke A. Sato, Angel Rubio

    Physical Review A　101　(1)　2020/01/15

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.101.012510 　

    ISSN： 2469-9926

    eISSN： 2469-9934

  54. Photovoltaic Effect from the Viewpoint of Time-reversal Symmetry Peer-reviewed

    Shunsuke A. Sato

    Journal of the Physical Society of Japan　88　(11)　115003-115003　2019/11/15

    Publisher: Physical Society of Japan

    DOI： 10.7566/jpsj.88.115003 　

    ISSN： 0031-9015

    eISSN： 1347-4073

  55. Light-induced anomalous Hall effect in massless Dirac fermion systems and topological insulators with dissipation Peer-reviewed

    S A Sato, P Tang, M A Sentef, U De Giovannini, H Hübener, A Rubio

    New Journal of Physics　21　(9)　093005-093005　2019/09/01

    Publisher: IOP Publishing

    DOI： 10.1088/1367-2630/ab3acf 　

    eISSN： 1367-2630

  56. Attosecond screening dynamics mediated by electron localization in transition metals Peer-reviewed

    M. Volkov, S. A. Sato, F. Schlaepfer, L. Kasmi, N. Hartmann, M. Lucchini, L. Gallmann, A. Rubio, U. Keller

    Nature Physics　15　(11)　1145-1149　2019/08/05

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41567-019-0602-9 　

    ISSN： 1745-2473

    eISSN： 1745-2481

  57. Charge Density Wave Melting in One-Dimensional Wires with Femtosecond Subgap Excitation Peer-reviewed

    M. Chávez-Cervantes, G. E. Topp, S. Aeschlimann, R. Krause, S. A. Sato, M. A. Sentef, I. Gierz

    Physical Review Letters　123　(3)　2019/07/19

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevlett.123.036405 　

    ISSN： 0031-9007

    eISSN： 1079-7114

  58. Microscopic theory for the light-induced anomalous Hall effect in graphene Peer-reviewed

    S. A. Sato, J. W. McIver, M. Nuske, P. Tang, G. Jotzu, B. Schulte, H. Hübener, U. De Giovannini, L. Mathey, M. A. Sentef, A. Cavalleri, A. Rubio

    Physical Review B　99　(21)　2019/06/10

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.99.214302 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  59. Nonlinear polarization evolution using time-dependent density functional theory Peer-reviewed

    Mitsuharu Uemoto, Yuki Kuwabara, Shunsuke A. Sato, Kazuhiro Yabana

    The Journal of Chemical Physics　150　(9)　2019/03/01

    Publisher: AIP Publishing

    DOI： 10.1063/1.5068711 　

    ISSN： 0021-9606

    eISSN： 1089-7690

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    We propose a theoretical and computational approach to investigate temporal behavior of a nonlinear polarization in a perturbative regime induced by an intense and ultrashort pulsed electric field. First-principles time-dependent density functional theory is employed to describe the electron dynamics. Temporal evolution of third-order nonlinear polarization is extracted from a few calculations of electron dynamics induced by pulsed electric fields with the same time profile but different amplitudes. We discuss characteristic features of the nonlinear polarization evolution as well as an extraction of nonlinear susceptibilities and time delays by fitting the polarization. We also carry out a decomposition of temporal and spatial changes in the electron density in power series with respect to the field amplitude. It helps to get insight into the origin of the nonlinear polarization in atomic scale.

  60. Theory for Electron Excitation in Dielectrics under an Intense Linear and Circularly Polarized Laser Fields Peer-reviewed

    Tomohito Otobe, Yasushi Shinohara, Shunsuke A. Sato, Kazuhiro Yabana

    Journal of the Physical Society of Japan　88　(2)　024706-024706　2019/02/15

    Publisher: Physical Society of Japan

    DOI： 10.7566/jpsj.88.024706 　

    ISSN： 0031-9015

    eISSN： 1347-4073

  61. Unraveling materials Berry curvature and Chern numbers from real-time evolution of Bloch states Peer-reviewed

    Dongbin Shin, Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Jeongwoo Kim, Noejung Park, Angel Rubio

    Proceedings of the National Academy of Sciences　116　(10)　4135-4140　2019/02/14

    Publisher: Proceedings of the National Academy of Sciences

    DOI： 10.1073/pnas.1816904116 　

    ISSN： 0027-8424

    eISSN： 1091-6490

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    Significance It was established by Thouless, Kohmoto, Nightingale, and den Nijs in 1982 that the topology of the solid-state wavefunctions leads to quantization of transverse electrical conductivity of an insulator. This recognition has led to the development of the new field of topological materials characterized by symmetry-protected quantum numbers. Here, we propose a general and computationally efficient framework enabling one to unveil and predict materials-topological invariants in terms of physical observables, such as the bulk time-dependent current. We show how the quantized charge and spin Hall effect appears even for materials with a non-Abelian Berry phase. This dynamical approach is not necessarily restricted to density functional theory, but can be extended to other schemes and to other methods dealing with correlations explicitly.

  62. SALMON: Scalable Ab-initio Light–Matter simulator for Optics and Nanoscience Peer-reviewed

    Masashi Noda, Shunsuke A. Sato, Yuta Hirokawa, Mitsuharu Uemoto, Takashi Takeuchi, Shunsuke Yamada, Atsushi Yamada, Yasushi Shinohara, Maiku Yamaguchi, Kenji Iida, Isabella Floss, Tomohito Otobe, Kyung-Min Lee, Kazuya Ishimura, Taisuke Boku, George F. Bertsch, Katsuyuki Nobusada, Kazuhiro Yabana

    Computer Physics Communications　235　356-365　2019/02

    Publisher: Elsevier BV

    DOI： 10.1016/j.cpc.2018.09.018 　

    ISSN： 0010-4655

  63. Ab Initio Simulation of Attosecond Transient Absorption Spectroscopy in Two-Dimensional Materials Peer-reviewed

    Shunsuke A. Sato, Hannes Hübener, Umberto De Giovannini, Angel Rubio

    Applied Sciences　8　(10)　1777-1777　2018/09/30

    Publisher: MDPI AG

    DOI： 10.3390/app8101777 　

    eISSN： 2076-3417

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    We extend the first-principles analysis of attosecond transient absorption spectroscopy to two-dimensional materials. As an example of two-dimensional materials, we apply the analysis to monolayer hexagonal boron nitride (h-BN) and compute its transient optical properties under intense few-cycle infrared laser pulses. Nonadiabatic features are observed in the computed transient absorption spectra. To elucidate the microscopic origin of these features, we analyze the electronic structure of h-BN with density functional theory and investigate the dynamics of specific energy bands with a simple two-band model. Finally, we find that laser-induced intraband transitions play a significant role in the transient absorption even for the two-dimensional material and that the nonadiabatic features are induced by the dynamical Franz–Keldysh effect with an anomalous band dispersion.

  64. Role of intraband transitions in photocarrier generation Peer-reviewed

    Shunsuke A. Sato, Matteo Lucchini, Mikhail Volkov, Fabian Schlaepfer, Lukas Gallmann, Ursula Keller, Angel Rubio

    Physical Review B　98　(3)　2018/07/05

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.98.035202 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  65. First-principles simulations for attosecond photoelectron spectroscopy based on time-dependent density functional theory Peer-reviewed

    Shunsuke A. Sato, Hannes Hübener, Angel Rubio, Umberto De Giovannini

    The European Physical Journal B　91　(6)　2018/06/22

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1140/epjb/e2018-90108-7 　

    ISSN： 1434-6028

    eISSN： 1434-6036

  66. Performance Optimization and Evaluation of Scalable Optoelectronics Application on Large Scale KNL Cluster Peer-reviewed

    Yuta Hirokawa, Taisuke Boku, Mitsuharu Uemoto, Shunsuke A. Sato, Kazuhiro Yabana

    Lecture Notes in Computer Science　205-225　2018/05/29

    Publisher: Springer International Publishing

    DOI： 10.1007/978-3-319-92040-5_11 　

    ISSN： 0302-9743

    eISSN： 1611-3349

  67. Velocity-gauge real-time TDDFT within a numerical atomic orbital basis set Peer-reviewed

    C.D. Pemmaraju, F.D. Vila, J.J. Kas, S.A. Sato, J.J. Rehr, K. Yabana, David Prendergast

    Computer Physics Communications　226　30-38　2018/05

    Publisher: Elsevier BV

    DOI： 10.1016/j.cpc.2018.01.013 　

    ISSN： 0010-4655

  68. Coupled forward-backward trajectory approach for nonequilibrium electron-ion dynamics Peer-reviewed

    Shunsuke A. Sato, Aaron Kelly, Angel Rubio

    Physical Review B　97　(13)　2018/04/25

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.97.134308 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  69. Attosecond optical-field-enhanced carrier injection into the GaAs conduction band Peer-reviewed

    F. Schlaepfer, M. Lucchini, S. A. Sato, M. Volkov, L. Kasmi, N. Hartmann, A. Rubio, L. Gallmann, U. Keller

    Nature Physics　14　(6)　560-564　2018/03/12

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/s41567-018-0069-0 　

    ISSN： 1745-2473

    eISSN： 1745-2481

  70. Performance Evaluation of Large Scale Electron Dynamics Simulation under Many-core Cluster based on Knights Landing Peer-reviewed

    Yuta Hirokawa, Taisuke Boku, Shunsuke A. Sato, Kazuhiro Yabana

    Proceedings of the International Conference on High Performance Computing in Asia-Pacific Region　183-191　2018/01/28

    Publisher: ACM

    DOI： 10.1145/3149457.3149465 　

  71. Ab initio multiscale simulation of high-order harmonic generation in solids Peer-reviewed

    Isabella Floss, Christoph Lemell, Georg Wachter, Valerie Smejkal, Shunsuke A. Sato, Xiao-Min Tong, Kazuhiro Yabana, Joachim Burgdörfer

    Physical Review A　97　(1)　2018/01/16

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.97.011401 　

    ISSN： 2469-9926

    eISSN： 2469-9934

  72. First-principles calculations for initial electronic excitation in dielectrics induced by intense femtosecond laser pulses Peer-reviewed

    Shunsuke A. Sato, Kazuhiro Yabana

    SPIE Proceedings　10014　100141A-100141A　2016/12/06

    Publisher: SPIE

    DOI： 10.1117/12.2243012 　

    ISSN： 0277-786X

  73. Attosecond dynamical Franz-Keldysh effect in polycrystalline diamond Peer-reviewed

    M. Lucchini, S. A. Sato, A. Ludwig, J. Herrmann, M. Volkov, L. Kasmi, Y. Shinohara, K. Yabana, L. Gallmann, U. Keller

    Science　353　(6302)　916-919　2016/08/26

    Publisher: American Association for the Advancement of Science (AAAS)

    DOI： 10.1126/science.aag1268 　

    ISSN： 0036-8075

    eISSN： 1095-9203

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    Shining a fast light on diamonds Conceptually, the electronic structure of matter is a fixed scaffold of energy levels, which electrons climb with the help of light absorption. In reality, the light's electromagnetic field distorts the scaffold, a phenomenon that becomes increasingly evident with rising field intensity. Lucchini et al. studied a manifestation of this phenomenon, termed the dynamical Franz Keldysh effect, in diamond substrates exposed to sudden, moderately intense infrared fields. Using attosecond probe pulses and accompanying theoretical simulations, they resolved and accounted for the extremely rapid ensuing electron dynamics. Science , this issue p. 916

  74. Attosecond nonlinear polarization and light–matter energy transfer in solids Peer-reviewed

    A. Sommer, E. M. Bothschafter, S. A. Sato, C. Jakubeit, T. Latka, O. Razskazovskaya, H. Fattahi, M. Jobst, W. Schweinberger, V. Shirvanyan, V. S. Yakovlev, R. Kienberger, K. Yabana, N. Karpowicz, M. Schultze, F. Krausz

    Nature　534　(7605)　86-90　2016/05/23

    Publisher: Springer Science and Business Media LLC

    DOI： 10.1038/nature17650 　

    ISSN： 0028-0836

    eISSN： 1476-4687

  75. Femtosecond time-resolved dynamical Franz-Keldysh effect Peer-reviewed

    T. Otobe, Y. Shinohara, S. A. Sato, K. Yabana

    Physical Review B　93　(4)　2016/01/21

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.93.045124 　

    ISSN： 2469-9950

    eISSN： 2469-9969

  76. Controlling ultrafast currents by the nonlinear photogalvanic effect Peer-reviewed

    Georg Wachter, Shunsuke A Sato, Isabella Floss, Christoph Lemell, Xiao-Min Tong, Kazuhiro Yabana, Joachim Burgdörfer

    New Journal of Physics　17　(12)　123026-123026　2015/12/21

    Publisher: IOP Publishing

    DOI： 10.1088/1367-2630/17/12/123026 　

    eISSN： 1367-2630

  77. Protocol for observing molecular dipole excitations by attosecond self-streaking Peer-reviewed

    Georg Wachter, Stefan Nagele, Shunsuke A. Sato, Renate Pazourek, Michael Wais, Christoph Lemell, Xiao-Min Tong, Kazuhiro Yabana, Joachim Burgdörfer

    Physical Review A　92　(6)　2015/12/18

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.92.061403 　

    ISSN： 1050-2947

    eISSN： 1094-1622

  78. Nonlinear electronic excitations in crystalline solids using meta-generalized gradient approximation and hybrid functional in time-dependent density functional theory Peer-reviewed

    Shunsuke A. Sato, Yasutaka Taniguchi, Yasushi Shinohara, Kazuhiro Yabana

    The Journal of Chemical Physics　143　(22)　2015/12/14

    Publisher: AIP Publishing

    DOI： 10.1063/1.4937379 　

    ISSN： 0021-9606

    eISSN： 1089-7690

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    We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.

  79. Time-dependent density functional theory of high-intensity short-pulse laser irradiation on insulators Peer-reviewed

    S. A. Sato, K. Yabana, Y. Shinohara, T. Otobe, K.-M. Lee, G. F. Bertsch

    Physical Review B　92　(20)　2015/11/12

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.92.205413 　

    ISSN： 1098-0121

    eISSN： 1550-235X

  80. Application of norm-conserving pseudopotentials to intense laser-matter interactions Peer-reviewed

    Xiao-Min Tong, Georg Wachter, Shunsuke A. Sato, Christoph Lemell, Kazuhiro Yabana, Joachim Burgdörfer

    Physical Review A　92　(4)　2015/10/29

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physreva.92.043422 　

    ISSN： 1050-2947

    eISSN： 1094-1622

  81. Attosecond band-gap dynamics in silicon Peer-reviewed

    Martin Schultze, Krupa Ramasesha, C.D. Pemmaraju, S.A. Sato, D. Whitmore, A. Gandman, James S. Prell, L. J. Borja, D. Prendergast, K. Yabana, Daniel M. Neumark, Stephen R. Leone

    Science　346　(6215)　1348-1352　2014/12/12

    Publisher: American Association for the Advancement of Science (AAAS)

    DOI： 10.1126/science.1260311 　

    ISSN： 0036-8075

    eISSN： 1095-9203

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    Electron transfer from valence to conduction band states in semiconductors is the basis of modern electronics. Here, attosecond extreme ultraviolet (XUV) spectroscopy is used to resolve this process in silicon in real time. Electrons injected into the conduction band by few-cycle laser pulses alter the silicon XUV absorption spectrum in sharp steps synchronized with the laser electric field oscillations. The observed ~450-attosecond step rise time provides an upper limit for the carrier-induced band-gap reduction and the electron-electron scattering time in the conduction band. This electronic response is separated from the subsequent band-gap modifications due to lattice motion, which occurs on a time scale of 60 ± 10 femtoseconds, characteristic of the fastest optical phonon. Quantum dynamical simulations interpret the carrier injection step as light-field–induced electron tunneling.

  82. Dielectric response of laser-excited silicon at finite electron temperature Peer-reviewed

    S. A. Sato, Y. Shinohara, T. Otobe, K. Yabana

    Physical Review B　90　(17)　2014/11/11

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.90.174303 　

    ISSN： 1098-0121

    eISSN： 1550-235X

  83. Ab InitioSimulation of Electrical Currents Induced by Ultrafast Laser Excitation of Dielectric Materials Peer-reviewed

    Georg Wachter, Christoph Lemell, Joachim Burgdörfer, Shunsuke A. Sato, Xiao-Min Tong, Kazuhiro Yabana

    Physical Review Letters　113　(8)　2014/08/18

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevlett.113.087401 　

    ISSN： 0031-9007

    eISSN： 1079-7114

  84. Efficient basis expansion for describing linear and nonlinear electron dynamics in crystalline solids Peer-reviewed

    Shunsuke A. Sato, Kazuhiro Yabana

    Physical Review B　89　(22)　2014/06/30

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.89.224305 　

    ISSN： 1098-0121

    eISSN： 1550-235X

  85. Numerical pump-probe experiments of laser-excited silicon in nonequilibrium phase Peer-reviewed

    S. A. Sato, K. Yabana, Y. Shinohara, T. Otobe, G. F. Bertsch

    Physical Review B　89　(6)　2014/02/10

    Publisher: American Physical Society (APS)

    DOI： 10.1103/physrevb.89.064304 　

    ISSN： 1098-0121

    eISSN： 1550-235X

  86. First-principles simulation of the optical response of bulk and thin-film α-quartz irradiated with an ultrashort intense laser pulse Peer-reviewed

    Kyung-Min Lee, Chul Min Kim, Shunsuke A. Sato, Tomohito Otobe, Yasushi Shinohara, Kazuhiro Yabana, Tae Moon Jeong

    Journal of Applied Physics　115　(5)　2014/02/07

    Publisher: AIP Publishing

    DOI： 10.1063/1.4864662 　

    ISSN： 0021-8979

    eISSN： 1089-7550

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    A computational method based on a first-principles multiscale simulation has been used for calculating the optical response and the ablation threshold of an optical material irradiated with an ultrashort intense laser pulse. The method employs Maxwell's equations to describe laser pulse propagation and time-dependent density functional theory to describe the generation of conduction band electrons in an optical medium. Optical properties, such as reflectance and absorption, were investigated for laser intensities in the range 1010 W/cm2 to 2 × 1015 W/cm2 based on the theory of generation and spatial distribution of the conduction band electrons. The method was applied to investigate the changes in the optical reflectance of α-quartz bulk, half-wavelength thin-film, and quarter-wavelength thin-film and to estimate their ablation thresholds. Despite the adiabatic local density approximation used in calculating the exchange–correlation potential, the reflectance and the ablation threshold obtained from our method agree well with the previous theoretical and experimental results. The method can be applied to estimate the ablation thresholds for optical materials, in general. The ablation threshold data can be used to design ultra-broadband high-damage-threshold coating structures.

  87. Maxwell + TDDFT multi-scale simulation for laser-matter interactions Peer-reviewed

    Shunsuke A. Sato, Kazuhiro Yabana

    Journal of Advanced Simulation in Science and Engineering　1　(1)　98-110　2014

    Publisher: Japan Society for Simulation Technology

    DOI： 10.15748/jasse.1.98 　

    eISSN： 2188-5303

  88. Nonadiabatic generation of coherent phonons Peer-reviewed

    Y. Shinohara, S. A. Sato, K. Yabana, J.-I. Iwata, T. Otobe, G. F. Bertsch

    The Journal of Chemical Physics　137　(22)　2012/08/17

    Publisher: AIP Publishing

    DOI： 10.1063/1.4739844 　

    ISSN： 0021-9606

    eISSN： 1089-7690

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    The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonons, despite its unsatisfactory performance on reproducing the observed dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent phonon generation is also examined and compared with the TDDFT calculations.

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Misc. 1

  1. 高強度超短パルスレーザーと誘電体の相互作用を記述する第一原理計算

    矢花一浩, 佐藤駿丞, 篠原康, 乙部智仁

    固体物理 Vol.52 No.3　52　(3)　139-148　2017/03

    Publisher: アグネ技術センター

    ISSN： 0454-4544

Presentations 5

  1. First-Principles Electron Dynamics Simulations of Attosecond Phenomena in Solids Invited

    Shunsuke A. Sato

    Numerical Methods in Quantum Chemistry 2025

  2. Quantum Electron Dynamics Simulation for Attosecond Phenomena Invited

    Shunsuke A. Sato

    Strong Matter-Field Interactions and Breakthrough Simulations of Future Semiconductor, UNIST, Ulsan, South Korea　2024/11/15

  3. Quantum Electron Dynamics Calculation for Attosecond Phenomena Invited

    Shunsuke A. Sato

    The 2nd International Conference on Nonequilibrium and Ultrafast Quantum States (NUQS-2024), Songshan Lake Materials Laboratory, Dongguan, China　2024/10/25

  4. First-principles electron dynamics calculations for light-induced ultrafast phenomena Invited

    Shunsuke A. Sato

    ALTA 2024　2024/05/02

  5. First-principles electron dynamics calculations for light-induced ultrafast phenomena Invited

    Shunsuke A. Sato

    ALTA 2024, Seogwipo KAL Hotel, Jeju, Korea　2024/05/03

Research Projects 8

  1. Development of Attosecond Light-Driven Electronic Properties

    Offer Organization: Japan Society for the Promotion of Science

    System: Grants-in-Aid for Scientific Research

    Category: Grant-in-Aid for Scientific Research (C)

    Institution: Tohoku University

    2025/04/01 - 2029/03/31

  2. Realization of phonon strong coupling states using THz metamaterial resonators and their application to material property control

    Hirori Hideki

    Offer Organization: Japan Society for the Promotion of Science

    System: Grants-in-Aid for Scientific Research

    Category: Grant-in-Aid for Scientific Research (B)

    Institution: Kyoto University

    2021/04/01 - 2025/03/31

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    This study quantitatively clarifies the conditions for achieving ultrastrong coupling (USC) by adjusting the gap size of an optical resonator in the terahertz frequency range, thereby enhancing phonon-photon interactions. Experiments and numerical simulations demonstrated that reducing the gap size significantly amplifies the vacuum electric field within the cavity, strengthening its interaction with phonons. One of the key findings is that USC with the TO phonon mode of MAPbI3; was successfully achieved at a gap size of 0.1 μm, leading to a notable increase in coupling strength. This breakthrough enables precise control of phonon-photon polaritons at the nanoscale, providing a solid foundation for applications in quantum optics and material science. The results pave the way for advanced optical devices and quantum information technologies, offering new opportunities for phonon mode engineering and material control.

  3. THzメタマテリアル共振器によるフォノン強結合状態の実現と物性制御への応用

    廣理 英基, 佐藤 駿丞

    Offer Organization: 日本学術振興会

    System: 科学研究費助成事業 基盤研究(B)

    Category: 基盤研究(B)

    Institution: 京都大学

    2021/04/01 - 2025/03/31

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    「光による物性制御、及び新奇な物性の創発」は光物性物理分野の究極の目標の一つである。従来の高強度な光(レーザー)による物質駆動では、光から物質へのエネルギー移行に伴う熱の発生や破壊現象の誘発、あるいは散逸によるコヒーレンスの消失等の問題があり応用へ向けて解決すべき課題がある。本研究では、テラヘルツ（THz）周波数帯の「電磁場の量子揺らぎ」（ゼロ点振動場）を、金属メタマテリアル共振器（キャビティ）を通して閉じ込め、物質中のフォノン（格子振動）やマグノン（スピンの集団運動）との強結合状態を実現することで物性の制御を目指している。R３年度は、ハロゲン化ペロブスカイト半導体のCH3NH3PbI3の0.95THzのフォノン（Pb-I-Pb結合の振動）をナノ構造の分割リング共鳴器（SRR）で真空光子に結合し、最後にSRRのギャップを100nmに狭めていわゆる超強結合の実現を目指し、強いフォノン吸収（TOフォノン）をもつペロブスカイト半導体MAPbI3試料上にキャビティ強結合するリング型の金属メタマテリアル構造を試作した。結合強度を調べるために、ペロブスカイト膜でコーティングしたSRRの透過スペクトルを検出するTHz分光法の構築を行った。SRRの吸収ピークの周波数がフォノン周波数と等しいときにラビ分裂を観測した。

  4. 固体からの高次高調波発生の微視的機構に関する研究

    Offer Organization: 京都大学化学研究所

    System: 令和6年度国際共同利用・共同研究

    2024/04 - 2025/03

  5. 光駆動非平衡定常状態を利用した物性制御理論の構築

    Offer Organization: 光科学技術研究振興財団

    System: 研究助成

    2024/01 - 2024/12

  6. First principles investigation on optical-control of electronic structure

    Sato Shunsuke

    Offer Organization: Japan Society for the Promotion of Science

    System: Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists

    Category: Grant-in-Aid for Early-Career Scientists

    Institution: University of Tsukuba

    2020/04/01 - 2024/03/31

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    In this study, to achieve flexible control of electronic states using light, we analyzed the nonequilibrium and nonlinear dynamics of electrons driven by light in materials through first-principles electronic calculations based on time-dependent density functional theory and quantum dynamics calculations based on the quantum master equation. As a result, we found that under high-intensity light, the optical and transport properties of materials change at ultrafast speeds, and we elucidated the microscopic physical processes behind these property changes, such as changes in electronic states and occupancy effects.

  7. First-principles investigation of the photovoltaic effect in ferroelectrics Competitive

    Offer Organization: Alexander von Humboldt Foundation

    System: Humboldt Research Fellowship for Postdoctoral Researchers

    Institution: Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany

    2017/06 - 2019/05

  8. アト秒電子ダイナミクスの第一原理計算

    佐藤 駿丞

    Offer Organization: 日本学術振興会

    System: 科学研究費助成事業 特別研究員奨励費

    Category: 特別研究員奨励費

    Institution: 筑波大学

    2014/04/25 - 2017/03/31

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    平成28年度は、高強度・超短パルス光と物質の相互作用によっておこる極限的な非線形現象を微視的に理解するための理論的解析を行い、特に次の研究で成果があった。 (i)高強度フェムト秒レーザーが誘電体に誘起する超高速光学特性変化の第一原理計算 この研究では、国外の実験グループとの共同研究により、高強度なフェムト秒パルスレーザーが引き起こす誘電体の超高速な光学特性の変化を調べた。 特に、ダイアモンド薄膜に対する実験結果の理論解析においては、第一原理計算によって実験で観測される超高速光学特性変化を定量的によく再現することに成功した。さらに、ダイアモンドにおける超高速光学特性変化の微視的起源を明らかにするため、理論計により得られた情報をの詳細な解析を進めた。その結果、実験で観測された超高速な光学特性の変化は、高強度フェムト秒レーザーがダイアモンドの特定のバンド構造に引き起こすバンド内遷移(intra-band transition)に起因する動的Franz-Keldysh効果であることを明らかとなった。 この成果は、論文"Attosecond dynamical Franz-Keldysh effect in polycrystalline diamond", Science 353, 916 (2016) としてScience誌から発表されている。 また、さらにこの共同研究を発展させ、異なる物質・条件の下での超高速光学特性変化を実験と理論の両面から調べることにより、高強度超短パルスが引き起こすバンド内遷移、及びバンド間遷移(inter-band transition)からの異なる寄与の両方が超高速光学特性変化に対して重要な役割を果たすことが明らかとなってきた。

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