Excitation signatures of isochorically heated electrons in solids at finite wavenumber explored from first principles

TL;DR

This study uses first-principles simulations to explore how ultrafast electronic heating affects the dynamic structure factor in solids like aluminium and silicon, revealing new spectral features relevant for X-ray scattering experiments.

Contribution

It provides a detailed first-principles analysis of electronic heating effects on the dynamic structure factor at finite wavenumber in solids, predicting observable spectral signatures.

Findings

Thermally induced red shift of plasmon in Al and Si.

Formation of a double-plasmon peak in Al due to Landau damping.

Distinct peak-valley structure in Si's DSF at small frequencies.

Abstract

Ultrafast heating of solids with modern X-ray free electron lasers (XFELs) leads to a unique set of conditions that is characterized by the simultaneous presence of heated electrons in a cold ionic lattice. In this work, we analyze the effect of electronic heating on the dynamic structure factor (DSF) in bulk Aluminium (Al) with a face-centered cubic lattice and in silicon (Si) with a crystal diamond structure using first-principles linear-response time-dependent density functional theory simulations. We find a thermally induced red shift of the collective plasmon excitation in both materials. In addition, we show that the heating of the electrons in Al can lead to the formation of a double-plasmon peak due to the extension of the Landau damping region to smaller wavenumbers. Finally, we demonstrate that thermal effects generate a measurable and distinct signature (peak-valley structure) in the DSF of Si at small frequencies. Our simulations indicate that there is a variety of new features in the spectrum of X-ray-driven solids, specifically at finite momentum transfer, which can probed in upcoming X-ray Thomson scattering (XRTS) experiments at various XFEL facilities.