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

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

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

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 $\delta$ of the population in momentum space. When $\delta\sim\pi$, the shifted population relaxes to a negative-temperature state, which leads to the interaction switching. Due to electron correlation effects $\delta$ deviates from the dynamical phase $\phi=\int dt F(t)$, which enables the seemingly counterintuitive repulsion-to-attraction transition by a monocycle pulse with $\phi=0$.Comment: 6 pages, 6 figure

Changes in Mitochondrial Spectra of Submerged Rice Seedlings after Exposure to Air Gaussian Deconvolution Analysis

Quantitative changes in mitochondrial cytochromes of submerged rice seedlings after exposure to air were investigated using gaussian deconvolution analysis on absorption spectrum at liquid nitrogen temperature. Differnece spectra were obtained from subtracting the absorption spectra of oxidized mitochondria from reduced mitochondria by succinate with antimycin-A. they showed three kinds of b-type cytochrome and a spectral component similar to cytochrome c1. Subtraction of the cytochrome c1-like component from the spectrum by curve analysis showed that three cytochrome bs had similar absorption maximum and that on a mitochondrial protein basis they were constant during air-adaptation. Cytochrome c per mitochontorial protein in submerged seedlings was about half of that in aerobic seedlings and increased by 1.5-fold during air-adaptation. The change in cytochrome c content was in paralleled with that of cytochrome aa3. These findings revealed that there were two groups of cytochromes in the response to air-adaptation,i.e.,three cytochrome bs were constant and cytochoromes c and aa3 increased in parallel.吸収スペクトルをカーブアナリシスの手法を用いて解析し、水中で発芽した芽生えが空気に触れたときに生じるミトコンドリアチトクロム類の量的変化を調べた。アンチマンイシンA存在下でのコハク酸還元による差スペクトルには3種のチトクロムbが見出されるが、チトクロムc1とよく似た成分がかなりの寄与で存在していることが判った。その寄与を除くといずれの芽生えから単離したミトコンドリアにおいても、3種のチトクロムbは互いにほとんど同程度の吸収を示した。また、水中芽生え、酸素適応芽生え、好気芽生えから単離したミトコンドリアの間には、3種いずれのチトクロムbの吸収（タンパク質当たり）に関しても差がなかった。チトクロムcは水中芽生えでは好気芽生えの約半分の量が存在し、酸素適応過程で1.5倍に増加した。これはチトクロムaa3の変化と全く同じであった。チトクロム類の中には、酸素適応過程において酸素に対する応答の異なる2つのグループが存在することを示した

Nonequilibrium Steady State of Photoexcited Correlated Electrons in the Presence of Dissipation

We present a framework to determine nonequilibrium steady states in strongly correlated electron systems in the presence of dissipation. This is demonstrated for a correlated electron (Falicov-Kimball) model attached to a heat bath and irradiated by an intense pump light, for which an exact solution is obtained with the Floquet method combined with the nonequilibrium dynamical mean-field theory. On top of a Drude-like peak indicative of photometallization as observed in recent pump-probe experiments, new nonequilibrium phenomena are predicted to emerge, where the optical conductivity exhibits dip and kink structures around the frequency of the pump light, a midgap absorption arising from photoinduced Floquet subbands, and a negative attenuation (gain) due to a population inversion.Comment: 5 pages, 3 figures, published versio