Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 12: CE: Metal-Insulator Transition 1

TT 12.1: Vortrag

Dienstag, 23. März 2010, 09:30–09:45, H19

Nonequilibrium Mott-Hubbard Systems Driven by External Laser Fields — •Andreas Lubatsch and Johann Kroha — Physikalisches Institut, Universität Bonn, 53115 Bonn, Germany

Mott-Hubbard insulating materials have the potential for use as ultrafast electric switches, driven by an external laser field, due to the short relaxation times characteristic for strongly correlated systems. We consider the Hubbard model at half filling, driven out of equilibrium by an external, time-periodic laser field. The vector nature of the external field and a gauge where the electric field couples to the dipole monent of the charge distribution, different from the “Peierls substitution” of previous authors’ work, is essential for obtaining the correct infrared behavior. We generalize the dynamical mean-field theory (DMFT) to nonequilibrium in a time-periodic driving field, using a Floquet mode representation and the Keldysh formalism. We calculate the nonequilibrium electron distribution function, the spectral density, nonequilibrium relaxation times and the DC conductivity in the presence of the external laser field for the metallic and for the insulating phase of the Hubbard model. In the metallic pseudo-gap phase, enhanced quantum coherence due to a polariton-like coupling of electronic excitations to the discrete electromagnetic mode is predicted. This leads to a revival of the many-particle resonance at the Fermi energy at resonant laser frequencies. In the Mott insulating (equilibrium) phase, an insulator-metal transition occurs as a function of the laser frequency, while the Mott-Hubbard gap remains rubust. This corresponds to nonequilibrium pumping into the upper Hubbard band.