Naoto Tsuji

The University of Tokyo

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Hideo Aoki

The University of Tokyo

Philipp Werner

University of Fribourg

Takashi Oka

The University of Tokyo

Yuta Murakami

Niigata University of Health and Welfare

Martin Eckstein

Universität Hamburg

Masahito Ueda

The University of Tokyo

Masaya Nakagawa

The University of Tokyo

Hideaki Sakata

Kawagoe Technical High School

Ryo Shimano

The University of Tokyo

Takuya Kato

Idemitsu Kosan (Japan)

Cooperative Institutions

The University of Tokyo

Tokyo University of Science

Japan Science and Technology Agency

Max Planck Institute for Solid State Research

Kyoto University

Osaka University

RIKEN Center for Emergent Matter Science

Tohoku University

National Institute of Advanced Industrial Science and Technology

Max Planck Society

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Floquet States

arXiv (Cornell University) (2023)

Naoto Tsuji

Quantum systems driven by a time-periodic field are a platform of condensed matter physics where effective (quasi)stationary states, termed "Floquet states", can emerge with external-field-dressed quasiparticles during driving. They appear, for example, as a prethermal intermediate state in isolated driven quantum systems or as a nonequilibrium steady state in driven open quantum systems coupled to environment. Floquet states may have various intriguing physical properties, some of which can be drastically different from those of the original undriven systems in equilibrium. In this article, we review fundamental aspects of Floquet states, and discuss recent topics and applications of Floquet states in condensed matter physics.

Floquet theory

10.48550/arxiv.2301.12676

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Citations (3)

Physical Review B (2008)

Naoto Tsuji Takashi Oka Hideo Aoki

We propose to combine the Floquet formalism for systems in ac fields with the dynamical mean-field theory to study correlated electron systems periodically driven out of equilibrium by external fields such as intense laser light. This approach has a virtue that we can nonperturbatively include both the correlation effects and nonlinear effects due to the driving field, which is imperative in analyzing recent experiments for photoinduced phase transitions. In solving the problem, we exploit a general theorem that the Hamiltonian in a Floquet matrix form can be exactly diagonalized for single-band noninteracting systems. As a demonstration, we have applied the method to the Falicov-Kimball model in intense ac fields to calculate the spectral function. The result shows that photoinduced midgap states emerge from strong ac fields, triggering an insulator-metal transition.

Floquet theory

Hamiltonian (control theory)

Formalism (music)

Maxima and minima

10.1103/physrevb.78.235124

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Citations (172)

Nonequilibrium DMFT approach to time-resolved Raman spectroscopy

Physical review. B./Physical review. B (2023)

Philipp Werner Martin Eckstein Naoto Tsuji

Raman spectroscopy uses light scattering to extract information on low-energy excitations of solids. The Raman process is described by diagrams which are fourth order in the light-matter interaction and in particular the resonant contribution, which involves four different space-time arguments, is difficult to evaluate. If one instead simulates explicitly the incoming (classical) light pulse, the Raman signal is given by the outgoing photon flux and can be determined from a two-point correlation function. Such a formalism can be used to compute the time-resolved Raman spectrum of nonequilibrium systems, as well as nonlinear signals which are higher order in the incoming field, such as hyper-Raman scattering. Here we explain how to implement this time-dependent formalism within the dynamical mean field theory framework. The method is illustrated with applications to the Holstein-Hubbard model in the strong electron-phonon coupling regime. We demonstrate hyper-Raman scattering in measurements with strong probe fields and frequency mixing signals in the presence of a pump field and simulate the evolution of Stokes and anti-Stokes features after photoexcitations of metallic and Mott insulating systems.

Coherent spectroscopy

10.1103/physrevb.108.245157

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Dynamical mean-field analysis of ordered phases in the half-filled Holstein-Hubbard model

arXiv (Cornell University) (2013)

Yuta Murakami Philipp Werner Naoto Tsuji Hideo Aoki

We investigate ordered phases (s-wave superconducting (SC), antiferromagnetic (AF) and charge ordered (CO) phases) of the half-filled Holstein-Hubbard model using the dynamical mean-field theory in combination with a continuous time quantum Monte Carlo impurity solver. We particularly focus on the parameter regime where the electron-electron Coulomb interaction and the phonon mediated retarded attractive interaction are both comparable to the bare electron bandwidth to understand the interplay of these interactions and the retardation effects due to finite phonon frequency \omega_0. Results for the transition temperatures for SC and AF as a function of the effective interaction U_eff(=U-\lambda with U the Coulomb repulsion and \lambda the phonon-mediated attraction) show deviations from the the corresponding results in the anti-adiabatic limit. These are analyzed by comparing with an effective static model in the polaron picture. We also determine the phase diagram around U_eff=0 at low, but nonzero temperatures to show that paramagnetic phases appear between AF and CO when U and \lambda are small or large, while AF and CO directly compete with each other at moderate U and \lambda.

Mean field theory

Lattice (music)

10.48550/arxiv.1309.7554

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Light-driven interlayer propagation of collective-mode excitations in layered superconductors

arXiv (Cornell University) (2024)

Niklas Ziereis Kazuaki Takasan Naoto Tsuji

Superconductors exhibit a nonlinear interaction with an applied light, which can resonantly excite the collective amplitude (Higgs) mode. Here we study light-induced dynamics of layered superconductors, where each layer is coupled to adjacent layers via the Josephson coupling and the first few layers near the surface are driven by an in-plane-polarized light. We study the system under the assumption that the interlayer Coulomb interactions are sufficiently screened out and that the phase-difference mode becomes available in the low-energy regime. We find that interlayer transport is induced via excitations of the collective amplitude and phase-difference modes, even when the applied electric field is parallel to the planes. We provide analytic calculations as well as numerical simulations of the real-time dynamics, and investigate the influence on the light-induced interlayer Josephson current and intralayer third-harmonic generation.

Mode (computer interface)

10.48550/arxiv.2403.08734

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Nature of the superconducting fluctuations in photoexcited systems

Physical review. B./Physical review. B (2019)

Ryuta Iwazaki Naoto Tsuji Shintaro Hoshino

The photo-excited state associated with superconducting fluctuation above the superconducting critical temperature $T_c$ is studied based on the time-dependent Ginzburg-Laundau approach. The excited state is created by an electric-field pulse and is probed by a weak secondary external field, which is treated by the linear response theory mimicking pump-probe spectroscopy experiments. The behavior is basically controlled by two relaxation rates: one is $γ_1$ proportional to the temperature measured from the critical point $T - T_c$ and the other is $γ_2$ proportional to the excitation intensity of the pump pulse. The excited state approaches the equilibrium state exponentially in a long time $t \gg γ_1^{-1}$, while in the intermediate time domain we find a power-law or logarithmic decay with different exponents for $t\ll γ_2^{-1}$ and $γ_2^{-1} \ll t \ll γ_1^{-1}$, even though the system is located away from the critical point. This is interpreted as the critical point in equilibrium being extended to a finite region in the excited situation. The parameter dependences on both the pump and probe currents are also systematically studied in all dimensions.

Critical point (mathematics)

10.1103/physrevb.100.104521

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Citations (6)

Nonequilibrium giant loop currents and orbital magnetism in carbon nanotubes

Bulletin of the American Physical Society (2007)

Naoto Tsuji Shigehiro Takajo Hideo Aoki

Magnetism

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First-principles design of a half-filled flat band of the kagome lattice in two-dimensional metal-organic frameworks

Physical Review Letters (2016)

Masahiko Yamada Tomohiro Soejima Naoto Tsuji Daisuke Hirai Mircea Dincǎ

We design from first principles a type of two-dimensional metal-organic framework (MOF) using phenalenyl-based ligands to exhibit a half-filled flat band of the kagome lattice, which is one of a family of lattices that show Lieb-Mielke-Tasaki's flat-band ferromagnetism. Among various MOFs, we find that trans-Au-THTAP (THTAP=trihydroxytriaminophenalenyl) has such an ideal band structure, where the Fermi energy is adjusted right at the flat band due to unpaired electrons of radical phenalenyl. The spin-orbit coupling opens a band gap giving a nonzero Chern number to the nearly flat band, as confirmed by the presence of the edge states in first-principles calculations and by fitting to the tight-binding model. This is a novel and realistic example of a system in which a nearly flat band is both ferromagnetic and topologically nontrivial.

Lattice (music)

Fermi energy

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Erratum: Electronic structure of helicoidal graphene: Massless Dirac particles on a curved surface with a screw symmetry [Phys. Rev. B92, 205425 (2015)]

Physical Review B (2015)

Masataka Watanabe Hisato Komatsu Naoto Tsuji Hideo Aoki

Massless particle

10.1103/physrevb.92.239902

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Tachyonic and Plasma Instabilities of $η$-Pairing States Coupled to Electromagnetic Fields

arXiv (Cornell University) (2021)

Naoto Tsuji Masaya Nakagawa Masahito Ueda

Cooper pairs featuring a nonzero center-of-mass crystal momentum ${\boldsymbol Q}=(π,π, \dots)$ and an off-diagonal long-range order ($η$-pairing states) constitute exact eigenstates of a Hubbard model [C. N. Yang, Phys. Rev. Lett. 63, 2144 (1989)]. Here we show that the $η$-pairing states are rendered dynamically unstable via coupling to dynamical electromagnetic fields. The instability is caused by "tachyonic" electromagnetic fields and unstable plasma modes for attractive and repulsive interactions, respectively. The typical time scale of the growth of the instability is of the order of femtoseconds for electron systems in solids, which places a strict bound on the lifetime of the $η$-pairing states. The decay of the $η$-pairing states leads to enhanced light emission with frequencies shifted from the Hubbard interaction strength for the repulsive case and unattenuated electromagnetic penetration for the attractive case.

10.48550/arxiv.2103.01547

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Citations (3)