546 research outputs found

    FLEX+DMFT approach to the dd-wave superconducting phase diagram of the two-dimensional Hubbard model

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    The dynamical mean-field theory (DMFT) combined with the fluctuation exchange (FLEX) method, namely FLEX+DMFT, is an approach for correlated electron systems to incorporate both local and non-local long-range correlations in a self-consistent manner. We formulate FLEX+DMFT in a systematic way starting from a Luttinger-Ward functional, and apply it to study the dd-wave superconductivity in the two-dimensional repulsive Hubbard model. The critical temperature (TcT_c) curve obtained in the FLEX+DMFT exhibits a dome structure as a function of the filling, which has not been clearly observed in the FLEX approach alone. We trace back the origin of the dome to the local vertex correction from DMFT that renders a filling dependence in the FLEX self-energy. We compare the results with those of GW+DMFT, where the TcT_c-dome structure is qualitatively reproduced due to the same vertex correction effect, but a crucial difference from FLEX+DMFT is that TcT_c is always estimated below the N\'{e}el temperature in GW+DMFT. The single-particle spectral function obtained with FLEX+DMFT exhibits a double-peak structure as a precursor of the Hubbard bands at temperature above TcT_c.Comment: 8 pages, 7 figure

    Photoinduced insulator-metal transition in correlated electrons -- a Floquet analysis with the dynamical mean-field theory

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    In order to investigate photoinduced insulator-metal transitions observed in correlated electron systems, we propose a new theoretical method, where we combine a Floquet-matrix method for AC-driven systems with the dynamical mean-field theory. The method can treat nonequilibrium steady states exactly beyond the linear-response regime. We have applied the method to the Falicov-Kimball model coupled to AC electric fields, and numerically obtained the spectral function, the nonequilibrium distribution function and the current-voltage characteristic. The results show that intense AC fields indeed drive Mott-like insulating states into photoinduced metallic states in a nonlinear way.Comment: 4 pages, 3 figures, Proceedings of LT2

    Floquet States

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    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.Comment: 12 pages, 6 figures, prepared for Encyclopedia of Condensed Matter Physics, 2nd edition; minor revision is mad

    Repulsion-to-attraction transition in correlated electron systems triggered by a monocycle pulse

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    We study the time evolution of the Hubbard model driven by a half-cycle or monocycle pulsed electric field F(t) using the nonequilibrium dynamical mean-field theory. We find that for properly chosen pulse shapes the electron-electron interaction can be effectively and permanently switched from repulsive to attractive if there is no energy dissipation. The physics behind the interaction conversion is a nonadiabatic shift δ\delta of the population in momentum space. When δ∼π\delta\sim\pi, the shifted population relaxes to a negative-temperature state, which leads to the interaction switching. Due to electron correlation effects δ\delta deviates from the dynamical phase ϕ=∫dtF(t)\phi=\int dt F(t), which enables the seemingly counterintuitive repulsion-to-attraction transition by a monocycle pulse with ϕ=0\phi=0.Comment: 6 pages, 6 figure
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