Field-induced polaron formation in the Holstein-Hubbard model

We study the effect of strong DC and pulsed electric fields on a Mott insulating system with coupling to optical phonons. A DC field of the order of the gap induces a metallic state characterized by polaronic features in the gap region and a partially inverted population. In this quasi-steady state, the field-induced doublon-hole production is balanced by a phonon-enhanced doublon-hole recombination. The photo-excitation of carriers by a pulsed field leads to similar modifications of the electronic structure in the gap region, and an associated reduction of the doublon life-time. We demonstrate that the field-induced localization of electrons effectively enhances the phonon coupling, an effect which should be measureable with time-resolved photoemission spectroscopy

Ultrafast separation of photo-doped carriers in Mott antiferromagnets

We use inhomogeneous nonequilibrium dynamical mean-field theory to investigate the spreading of photo-excited carriers in Mott insulating heterostructures with strong internal fields. Antiferromagnetic correlations are found to affect the carrier dynamics in a crucial manner: An antiferromagnetic spin background can absorb energy from photo-excited carriers on an ultrafast timescale, thus enabling fast transport between different layers and the separation of electron and hole-like carriers, whereas in the paramagnetic state, carriers become localized in strong fields. This interplay between charge and spin degrees of freedom can be exploited to control the functionality of devices based on Mott insulating heterostructures with polar layers, e.g., for photovoltaic applications

Thermalization of a pump-excited Mott insulator

We use nonequilibrium dynamical mean-field theory in combination with a recently implemented strong-coupling impurity solver to investigate the relaxation of a Mott insulator after a laser excitation with frequency comparable to the Hubbard gap. The time evolution of the double occupancy exhibits a crossover from a strongly damped transient at short times towards an exponential thermalization at long times. In the limit of strong interactions, the thermalization time is consistent with the exponentially small decay rate for artificially created doublons, which was measured in ultracold atomic gases. When the interaction is comparable to the bandwidth, on the other hand, the double occupancy thermalizes within a few times the inverse bandwidth along a rapid thermalization path in which the exponential tail is absent. Similar behavior can be observed in time-resolved photoemission spectroscopy. Our results show that a simple quasi-equilibrium description of the electronic state breaks down for pump-excited Mott insulators characterized by strong interactions.Comment: 8 pages, 4 figure

Photo-induced gap closure in an excitonic insulator

We study the dynamical phase transition out of an excitonic insulator phase after photo-excitation using a time-dependent extension of the selfconsistent GW method. We connect the evolution of the photoemission spectra to the dynamics of the excitonic order parameter and identify two dynamical phase transition points marked by a slowdown in the relaxation: one critical point is connected with the trapping in a nonthermal state with reduced exciton density and the second corresponds to the thermal phase transition. The transfer of kinetic energy from the photoexcited carriers to the exciton condensate is shown to be the main mechanism for the gap melting. We analyze the low energy dynamics of screening, which strongly depends on the presence of the excitonic gap, and argue that it is difficult to interpret the static component of the screened interaction as the effective interaction of some low energy model. Instead we propose a phenomenological measure for the effective interaction which indicates that screening has minor effects on the low energy dynamics

Optimal ramp shapes for the fermionic Hubbard model in infinite dimensions

We use non-equilibrium dynamical mean field theory and a real-time diagrammatic impurity solver to study the heating associated with time-dependent changes of the interaction in a fermionic Hubbard model. Optimal ramp shapes U(t) which minimize the excitation energy are determined for an infinitesimal change. For ramp times of a few inverse hoppings, these optimal U(t) are strongly oscillating with a frequency determined by the bandwidth. We show that the scaled versions of the optimized ramps yield substantially lower temperatures than linear ramps even far outside the perturbative regime.Comment: Published versio