Time-resolved X-ray Spectroscopy from the Atomic Orbital Ground State Up

TL;DR

This paper presents simulations of time-resolved X-ray absorption and RIXS spectroscopies using a detailed atomic multiplet model, demonstrating their potential to reveal nonequilibrium electronic properties in quantum materials.

Contribution

The study introduces a comprehensive simulation framework for time-resolved X-ray spectroscopies applied to a generalized cluster model, aiding future experimental interpretation.

Findings

Simulated cross-sections for $3d^9$ and $3d^8$ configurations show charge transfer effects.

Time-resolved spectra reveal how pump-induced excitations modify ground and excited states.

The approach provides benchmarks for upcoming experimental studies in quantum materials.

Abstract

X-ray spectroscopy has been a key method to determine ground and excited state properties of quantum materials with atomic specificity. Now, new x-ray facilities are opening the door to the study of pump-probe x-ray spectroscopy - specifically time-resolved x-ray absorption (trXAS) and time-resolved resonant inelastic x-ray scattering (trRIXS). In this paper we will present simulations of each of these spectroscopies using a time-domain full atomic multiplet, charge transfer Hamiltonian, adapted to study the properties of a generalized cluster model including a central transition metal ion caged by ligand atoms in a planar geometry. The numerically evaluated trXAS and trRIXS cross-sections for representative electron configurations $3d^9$ and $3d^8$ demonstrate the insights that can be obtained from charge transfer pumping, and how this nonequilibrium process affects ground and excited state properties. The straightforward characterization of the excitations in these systems, based on our analysis of the simulations, can serve as a benchmark for future experiments, as access to these time-resolved spectroscopic techniques becomes more widely available.