# Theory for Time-Resolved Resonant Inelastic X-ray Scattering

## TL;DR

This paper develops a theoretical framework for time-resolved resonant inelastic X-ray scattering (tr-RIXS), enabling the study of real-time quasiparticle dynamics and spectrum evolution in materials during pump pulses.

## Contribution

The paper introduces a novel theory for explicitly evaluating time-resolved RIXS, applicable to non-interacting systems and capable of revealing real-time particle-hole dynamics.

## Key findings

- Spectrum analysis matches steady-state and Floquet predictions at high pump frequencies.
- Low-frequency pumps allow extraction of real-time particle-hole continuum dynamics.
- Theory verified through application to a non-interacting electronic system.

## Abstract

Time-resolved measurements of materials provide a wealth of information on quasiparticle dynamics, and have been the focus of optical studies for decades. In this paper, we develop a theory for explicitly evaluating time-resolved resonant inelastic X-ray scattering (tr-RIXS). We apply the theory to a non-interacting electronic system and reveal the particle-hole spectrum and its evolution during the pump pulse. With a high-frequency pump, the frequency and amplitude dependence analysis of the spectra agrees well with the steady-state assumptions and Floquet excitations. When the pump frequency is low, the spectrum extracts real-time dynamics of the particle-hole continuum in momentum space. These results verify the correctness of our theory and demonstrate the breadth of physical problems that tr-RIXS could shed light on.