Ultrafast entropy production in pump-probe experiments

TL;DR

This paper develops a framework for measuring ultrafast entropy production in laser-excited phonons, linking experimental data to thermodynamic properties in non-equilibrium materials.

Contribution

It introduces ultrafast stochastic thermodynamics for phonons and calculates entropy production from experimental X-ray scattering data.

Findings

Entropy production correlates with the phonon power spectrum.

Broad peaks in entropy production relate to displacement correlations.

Method applied to SrTiO₃ and KTaO₃ at various temperatures.

Abstract

The ultrafast control of materials has opened the possibility to investigate non-equilibrium states of matter with striking properties, such as transient superconductivity and ferroelectricity, ultrafast magnetization and demagnetization, as well as Floquet engineering. The characterization of the ultrafast thermodynamic properties within the material is key for their control and design. Here, we develop the ultrafast stochastic thermodynamics for laser-excited phonons. We calculate the entropy production and heat absorbed from experimental data for single phonon modes of driven materials from time-resolved X-ray scattering experiments where the crystal is excited by a laser pulse. The spectral entropy production is calculated for SrTiO$_3$ and KTaO$_3$ for different temperatures and reveals a striking relation with the power spectrum of the displacement-displacement correlation function by inducing a broad peak beside the eigenmode-resonance.