# Hund's coupling driven photo-carrier relaxation in the two-band Mott insulator

## TL;DR

This paper investigates how Hund's coupling influences the ultrafast relaxation of photo-induced carriers in a two-band Mott insulator, revealing unique dynamics absent in single-band models and relevant for multi-orbital materials.

## Contribution

It demonstrates the role of Hund's coupling in photo-carrier relaxation dynamics using nonequilibrium DMFT in a two-band Hubbard model, highlighting effects like thermal blocking and kinetic freezing.

## Key findings

- Relaxation time inversely proportional to Hund's coupling
- Photo-doping creates side-bands and multiple resonances
- Identification of thermal blocking and kinetic freezing effects

## Abstract

We study the relaxation dynamics of photo-carriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photo-doped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation driven by emission of local spin excitations with an inverse relaxation time proportional to the Hund's coupling. The photo-doping generates additional side-bands in the spectral function, and for strong Hund's coupling, the photo-doped population also splits into several resonances. The dynamics of the local many-body states reveals two effects, thermal blocking and kinetic freezing, which manifest themselves when the Hund's coupling becomes of the order of the temperature or the bandwidth, respectively. These effects, which are absent in the single-band Hubbard model, should be relevant for the interpretation of experiments on correlated materials with multiple active orbitals. In particular, the features revealed in the non-equilibrium energy distribution of the photo-carriers are experimentally accessible, and provide information on the role of the Hund's coupling in these materials.