Toshihiro Sato

RIKEN, Вако, Saitama, Japan

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Publications (8)11.79 Total impact

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    Toshihiro Sato · Hirokazu Tsunetsugu
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    ABSTRACT: Dynamics in a triangular-lattice Hubbard model is studied at half filling on the basis of the cluster dynamical mean field theory. Numerical calculations use a solver of the continuous-time quantum Monte Carlo method based on the strong-coupling expansion. We examine the change in the nearest-neighbor dynamical correlations of doublon and holon in the time domain with varying the Coulomb repulsion near the Mott transition. We demonstrate that the nearest-neighbor doublon-holon pair shows a strong attractive correlation, particularly in the insulating phase, while the nearest-neighbor doublon-doublon pair shows a repulsive correlation. Useful information is provided by the trajectories in the complex plane of the dynamical correlation functions. The short-time dynamics of the nearest-neighbor doublon and holon in the metallic phase indicates larger fluctuations than in the insulating phase. Their trajectories in the complex plane show that the short-time dynamics of the doublon-holon pair has an opposite behavior to that of the doublon-doublon pair. We find that their time scale of dynamics can be characterized by the period in which the phase rotates π around the long-time limit in both phases. In the long-time region, fluctuations persist up to a very long time in the metallic phase, while they quickly vanish in the insulating phase.
    Preview · Article · Dec 2015 · Physics Procedia
  • Source
    Toshihiro Sato · Hirokazu Tsunetsugu
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    ABSTRACT: We study the dynamics of doublon in the half-filled Hubbard model on the triangular lattice by using the cellular dynamical mean field theory. Investigating the nearest-neighbor dynamical correlations, we demonstrate that a nearest-neighbor doublon-holon pair shows a strong attraction, in particular in the insulating phase. We also calculate the on-site dynamical correlation of doublon and find that the life time of doublon is longer in the metallic phase than in the insulating phase. In the long-time region, the metallic phase has persistent fluctuations in various nearest-neighbor configurations, while the fluctuations are vanishingly small in the insulating phase. Obtained results indicate clear differences of dynamics of doublon between in the metallic and in the insulating phases.
    Preview · Article · Apr 2014 · Physical Review B
  • Toshihiro Sato · Kazumasa Hattori · Hirokazu Tsunetsugu
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    ABSTRACT: We numerically study electric transport near the Mott metal-insulator transition for the half-filled Hubbard model on a triangular lattice. Our approach is a cellular dynamical mean field theory (CDMFT) with a continuous-time QMC solver and we calculate optical conductivity including vertex corrections. The main issue is the variation of optical conductivity upon controlling Coulomb repulsion U for various temperatures. Near the Mott critical end point, a Drude peak on the metallic side smoothly continues to an ``ingap" peak emerging within the Hubbard gap on the insulating side. We find a critical power-law behavior in their U-dependence near the critical point. The obtained critical exponent 1/δ=0.15 of the optical weight differs from the exponent 1/δ=1/3 of the order parameter (double occupancy) in the CDMFT calculations. This discrepancy suggests that conductivity does not have the same scaling behavior as that for the order parameter[1]. [1]T. Sato, K. Hattori, and H. Tsunetsugu, J. Phys. Soc. Jpn. 81, 083703 (2012).
    No preview · Article · Mar 2013
  • Source
    Toshihiro Sato · Kazumasa Hattori · Hirokazu Tsunetsugu
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    ABSTRACT: We study electric transport near the Mott metal-insulator transition in a triangular-lattice Hubbard model at half filling. We calculate optical conductivity $\sigma(\omega)$ based on a cellular dynamical mean field theory including vertex corrections inside the cluster. Near the Mott critical end point, a Drude analysis in the metallic region suggests that the change in the Drude weight is important rather than that in the transport scattering rate for the Mott transition. In the insulating region, there emerges an "ingap" peak in $\sigma(\omega)$ at low $\omega$ near the Mott transition, and this smoothly connects to the Drude peak in the metallic region with decreasing Coulomb repulsion. We find that the weight of these peaks exhibits a power-law behavior upon controlling Coulomb repulsion at the critical temperature. The obtained critical exponent suggests that conductivity does not correspond to magnetization or energy density of the Ising universality class in contrast to several previous works.
    Full-text · Article · Dec 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We examine the validity of the projected Gross-Pitaevskii simulation by taking the two-dimensional homogeneous bosonic system as an example. The long-distance behaviors of the correlation function and equilibrium temperatures show good agreement with those of the quantum Monte Carlo calculations below temperatures near the Kosterlitz-Thouless transition. We find that in the projected Gross-Pitaevskii description, one needs to estimate the optimal wave-number cutoff in temperature. In the well-described region, the projected Gross-Pitaevskii equation presents reliable predictions for the long-wave bosonic components.
    No preview · Article · May 2012 · Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics
  • Source
    Toshihiro Sato · Kazumasa Hattori · Hirokazu Tsunetsugu
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    ABSTRACT: We study electric transport near the Mott metal-insulator transition. Optical conductivity of the half-filled Hubbard model on a triangular lattice is calculated based on a cellular dynamical mean field theory including vertex corrections inside the cluster. By investigating the spectrum at low frequencies, we find that a Drude peak on the metallic side smoothly connects to an "ingap" peak on the insulating side. The optical weight of these peaks exhibits a critical behavior with power-law near the Mott critical end point, $|D-D^*|\propto|U-U^*|^{1/\delta}$. We find that the critical exponent $1/\delta$ differs from the exponents in the thermodynamics.
    Full-text · Article · Nov 2011 · Journal of the Physical Society of Japan
  • Toshihiro Sato · Kazumasa Hattori · Hirokazu Tsunetsugu
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    ABSTRACT: We study optical conductivity of the one-band Hubbard model on a two-dimensional isotropic triangular lattice at half filling by using the cellular dynamical mean field theory and particularly investigate its behavior near the critical end point of the first order Mott transition. In the metallic phase, the enhancement of effective mass and the significant frequency dependence of scattering rate is identified near the Mott transition. From the results in the insulating state near the Mott transition, we find that the frequency dependence of optical conductivity decays quite smoothly toward zero frequency and exhibits a power-law-like behavior in an intermediate frequency region. We also study optical conductivity of the Hubbard model on a kagomé lattice near the critical end point of the Mott transition. It shows a larger incoherent peak both in the metallic and insulating phases and a stronger frequency dependence of effective mass and scattering rate.
    No preview · Article · Sep 2011 · Journal of Physics Conference Series
  • Toshihiro Sato · Takafumi Suzuki · Naoki Kawashima
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    ABSTRACT: We study the finite-temperature transition of the quasi-2D Bose gas in an uniaxially-compressed harmonic trap by numerically solving the projected Gross-Pitaevskii equation. Gradual emergence of superfluidity is confirmed by calculating the moment of inertia when a temperature decreases. By investigating the long-distance behavior of a phase correlation function, superfluid density gradually increases reflecting the development of the phase correlation around the center of the system. From these results, we obtain the evidence for the emergence of superfluidity in this system directly.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series