Enhancement of impact ionization in Hubbard clusters by disorder and next-nearest-neighbor hopping

We perform time-resolved exact diagonalization of the Hubbard model with time-dependent hoppings on small clusters of up to 12 sites. Here, the time dependence originates from a classic electromagnetic pulse, which mimics the impact of a photon. We investigate the behavior of the double occupation and spectral function after the pulse for different cluster geometries and onsite potentials. We find impact ionization in all studied geometries except for one-dimensional chains. Adding next-nearest-neighbor hopping to the model leads to a significant enhancement of impact ionization, as does disorder and geometric frustration of a triangular lattice.