Abstract

The strongly correlated nature of Mott insulating systems in contrast to semiconductors provides a promising pathways into the realization of a new generation of solar cells with efficiencies going beyond the Shockley-Queisser limit. The crucial mechanism behind this prediction is the process of impact ionization, in which a high energy charge carrier decays by exciting new charge carriers. By additionally applying an electric field to a Mott system that already has a non-zero charge carrier density, impact ionization can repeat itself, leading to a substantial grow in the number of charge carriers, a process which is referred to as the avalanche mechanism.
We study the real-time dynamics of a half filled, two dimensional Hubbard model with a repulsive on-site interaction in the Gaussian state approximation, where we recover the impact ionization process and unveil the avalanche mechanism.
The initial increase in charge carrier density due to impact ionization, as well as the relaxation into a pre-thermalized, metastable state is studied, where we find that even this metastable state has a substantial increase in charge carrier density over the initial state. For the avalanche mechanism, we analyze the dependence of the charge carrier production on peak field strength and the driving frequency, which it is found to be dictated by the Keldysh parameter, a parameter that describes the energy ratio between field strength and frequency, which naturally arises by considering the charge carrier displacement in the Brillouin zone.