Abstract
We study the non-equilibrium response of a 4x3 Hubbard model at U=8 under the influence of a short electric field pulse, with the main focus on multiple photon excitations and on the change of double occupancy after the pulse. The behavior mainly depends on the driving frequency of the electric field. The largest change of double occupancy occurs during the pulse. For frequencies below the Mott gap, we observe multiphoton excitations at large field intensities. For frequencies beyond the gap energy, there is a region where Auger recombination reduces the double occupancy after the pulse. Impact ionization (Multi Exciton Generation), namely a growing double occupancy after the pulse, occurs for frequencies larger than twice the Mott gap. From the Loschmidt amplitude we compute the eigenstate spectrum of the quantum state after the pulse, observing multiple distinct photon excitation peaks, in line with expectations from a quasiparticle picture. We introduce a technique with which we analyze the time evolution of double occupancy in each peak individually. The long-term behavior of the double occupancy almost only depends on the absorbed energy, and we explore the connection of this property to the Eigenstate Thermalization Hypothesis.
Highlights
One exciting area of research is the influence of photoexcitations on strongly correlated electron systems
We investigated the nonequilibrium response of a strongly correlated Mott insulator to a short light pulse, using exactdiagonalization based calculations on a 4 × 3 Hubbard model for a large range of light intensities and of photon energies
We calculated the eigenstate spectra of the nonequilibrium states, i.e., the probability distribution of the work done by the light pulse, as the Fourier transform of the Loschmidt amplitude
Summary
One exciting area of research is the influence of photoexcitations on strongly correlated electron systems. An interesting phenomenon that has been observed for many quantum systems is that the long time mean of the expectation value of an observable can tend to a value which depends only on the energy of the initial state This is the topic of the so called eigenstate thermalization hypothesis (ETH) [52,53]. The spectral function is time dependent [24,25,30,31,33,34,44,58,68,69,70,71,72] and there is a photoinduced insulator-metal transition in the Hubbard model in various setups [28,31,33,34,58,69,70,71,73,74,75] Such an insulator-metal transition has been observed in experiment in quasi-one- and two-dimensional materials [76,77,78,79,80,81]
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