Ultrafast X-ray Absorption Spectroscopy of Strongly Correlated Systems: Core Hole Effect

TL;DR

This paper develops a theoretical framework for ultrafast x-ray absorption spectroscopy in strongly correlated one-dimensional systems, revealing how core hole effects and pump-probe dynamics influence electronic states and phase transitions.

Contribution

It introduces a model for nonequilibrium x-ray absorption in correlated systems, incorporating core hole effects and pump-driven dynamics, providing new insights into electronic structure evolution.

Findings

Core hole creates a qualitative change in the spectrum.

The spectrum reveals charge gap and metal-insulator transition.

Driven states show metallic droplets around the core hole.

Abstract

In recent years, ultrafast pump-probe spectroscopy has provided insightful information about nonequilibrium dynamics of excitations in materials. In a typical experiment of time-resolved x-ray absorption spectroscopy, the systems are excited by a femtosecond laser pulse (pump pulse) followed by an x-ray (probe pulse) after a time delay to measure the absorption spectra of the photoexcited systems. We present a theory for nonequilibrium x-ray absorption spectroscopy in one-dimensional strongly correlated systems. The core hole created by x-ray is modeled as an additional effective potential of the core hole site which changes the spectrum qualitatively. In equilibrium, the spectrum reveals the charge gap at half-filling and the metal-insulator transition in the presence of the core hole effect. Furthermore, a pump-probe scheme is introduced to drive the system out of equilibrium before the x-ray probe. The effects of the pump pulse with varying frequencies, shapes and fluences are discussed for the dynamics of strongly correlated systems in and out of resonance. The spectrum indicates that the driven insulating state has a metallic droplet around the core hole. The rich structures of the nonequilibrium x-ray absorption spectrum give more insight into the dynamics of electronic structures.