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TT: Fachverband Tiefe Temperaturen

TT 23: Correlated Electrons: (General) Theory

TT 23.8: Vortrag

Mittwoch, 27. Februar 2008, 16:00–16:15, H 0104

Non-equilibrium Hubbard Model in an external, time-dependent field — •Andreas Lubatsch and Johann Kroha — Physikalisches Institut, Universitaet Bonn, Germany

Mott-Hubbard insulating materials have the potential to be used for ultrafast electric switches, driven by an external laser field, because of the short relaxation times characteristic for strongly correlated systems. We consider the Hubbard model at half filling, driven by an external, stationary laser field. This electromagnetic field couples to the dipole moment of the charge distribution in the system, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian, periodic in time (photo-induced hopping). We generalize the dynamical mean-field theory (DMFT) to this non-equilibrium situation, employing a Floquet expansion of the electron density in terms of higher harmonics of the time-periodic hopping amplitude within the Keldysh formalism. We calculate the non-equilibrium electron distribution function, the density of states and the DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott-Hubbard gap. The results demonstrate that the system can be switched from a Mott-Hubbard insulating state to a conducting state by the external field, which corresponds to photo-induced excitations into the upper Hubbard band.