# Time-Resolved Resonant Inelastic X-Ray Scattering in a Pumped Mott Insulator

## TL;DR

This paper develops a theoretical framework for time-resolved resonant inelastic x-ray scattering (trRIXS) to study charge excitations and collective modes in a pumped Mott insulator, revealing complex transient behaviors and nonlinear effects.

## Contribution

It introduces a simulation approach for trRIXS in a Hubbard model, enabling detailed analysis of out-of-equilibrium charge excitations and their origins in correlated systems.

## Key findings

- Photodoping activates charge degrees of freedom in Mott insulators.
- trRIXS characterizes dispersion and nonlinear effects of collective excitations.
- Theoretical foundation supports interpretation of ultrafast x-ray scattering experiments.

## Abstract

Collective excitations contain rich information about photoinduced transient states in correlated systems. In a Mott insulator, charge degrees of freedom are frozen, but can be activated by photodoping. The energy-momentum distribution of the charge excitation spectrum reflects the propagation of charge degrees of freedom, and provides information about the interplay among various intertwined instabilities on the time scale set by the pump. To reveal charge excitations out of equilibrium, we simulate time-resolved x-ray absorption and resonant inelastic x-ray scattering using a Hubbard model. After pumping, the former resolves photodoping, while the latter characterizes the formation, dispersion, weight, and nonlinear effects of collective excitations. Intermediate-state information from time-resolved resonant inelastic x-ray scattering (trRIXS) can be used to decipher the origin of these excitations, including bimagnons, Mott-gap excitations, doublon and single-electron in-gap states, and anti-Stokes relaxation during an ultrafast pump. This paper provides a theoretical foundation for existing and future trRIXS experiments.