Effect of lattice excitations on transient near edge X-ray absorption spectroscopy

TL;DR

This study demonstrates that transient near edge X-ray absorption spectroscopy (XAS) can detect and quantify lattice temperature changes in a heterostructure, revealing sensitivity to phononic excitations with picosecond resolution.

Contribution

It introduces a method combining XAS, ultrafast electron diffraction, and ab initio calculations to analyze lattice excitations and their spectral signatures.

Findings

XAS spectral changes correlate with lattice temperature increases

Spectral fine structure decreases uniformly at higher phononic temperatures

Transient XAS sensitivity to phonons is experimentally demonstrated

Abstract

Time-dependent and constituent-specific spectral changes in soft near edge X-ray spectroscopy (XAS) of an [Fe/MgO]$_8$ metal/insulator heterostructure upon laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining X-ray absorption spectroscopy with ultrafast electron diffraction measurements and ab initio calculations demonstrate that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near edge XAS to phonons is demonstrated.