Impact ionization and multiple photon absorption in the two-dimensional photoexcited Hubbard model

We study the nonequilibrium response of a 4 x 3 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 (multiexciton 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.

Automated summary

We study the behavior of a Hubbard model under the influence of a short electric field pulse, focusing on phenomena such as multiple photon excitations and changes in double occupancy. The behavior depends on the driving frequency of the electric field. We observe distinct photon excitation peaks in the eigenstate spectrum, and introduce a technique to analyze the time evolution of double occupancy. The long-term behavior of double occupancy is mainly determined by the absorbed energy.