Photo-excited states in correlated band insulators

TL;DR

This paper investigates the non-equilibrium dynamics of correlated band insulators post-photo-excitation, revealing distinct behaviors depending on the interaction strength relative to the band gap, and distinguishing correlated from simple band insulators.

Contribution

It introduces a dynamical distinction between correlated and band insulators based on their relaxation behavior after photo-excitation using non-equilibrium DMFT.

Findings

Weak interactions lead to non-thermal states with separate electron and hole distributions.

Strong interactions cause spectral modifications and rapid thermalization.

The crossover occurs when the interaction strength is comparable to the band gap.

Abstract

We study the photo-excitation dynamics of correlated band insulators, using non-equilibrium dynamical mean-field theory for the ionic Hubbard model. We find two distinct behaviors, depending on the ratio of the on-site interaction $U$ and the bare band gap $\Delta$. For small interactions, the relaxation is characterized by intra-band carrier scattering in relatively rigid bands, leading to a non-thermal intermediate state with separate thermal distributions of electrons and holes. This behavior can be viewed as typical for a band insulator with weak interactions. For larger interaction, on the other hand, we observe a strong modification of the electronic spectrum and a filling-in of the gap after photo-excitation, along with a rapid thermalization of the system. The two behaviors therefore provide a dynamical distinction of a correlated band insulator and a band-insulator, which can differ even when the spectra of the two systems are similar in equilibrium. The crossover happens when the interaction $U$ is comparable to $\Delta$.