Ultrafast lattice dynamics and electron-phonon coupling in platinum extracted with a global fitting approach for time-resolved polycrystalline diffraction data

TL;DR

This paper introduces a novel analysis method for time-resolved diffraction data to accurately determine electron-phonon coupling in platinum, revealing its fluence-independent behavior and advancing understanding of nonequilibrium lattice dynamics.

Contribution

A new two-step fitting approach for analyzing polycrystalline diffraction data that improves extraction of lattice dynamics and electron-phonon coupling parameters.

Findings

Electron-phonon coupling parameter G_ep in platinum is approximately 3.9×10^17 W/m^3K.

G_ep remains constant up to an absorbed energy density of 124 J/cm^3.

The method provides insights into phonon thermalization and lattice dynamics.

Abstract

Quantitative knowledge of electron-phonon coupling is important for many applications as well as for the fundamental understanding of nonequilibrium relaxation processes. Time-resolved diffraction provides direct access to this knowledge through its sensitivity to laser-induced lattice dynamics. Here, we present an approach for analyzing time-resolved polycrystalline diffraction data. A two-step routine is used to minimize the number of time-dependent fit parameters. The lattice dynamics are extracted by finding the best fit to the full transient diffraction pattern rather than by analyzing transient changes of individual Debye-Scherrer rings. We apply this approach to platinum, an important component of novel photocatalytic and spintronic applications, for which a large variation of literature values exists for the electron-phonon coupling parameter $G_\mathrm{ep}$. Based on the extracted evolution of the atomic mean squared displacement (MSD) and using a two-temperature model (TTM), we obtain $G_\mathrm{ep}=(3.9\pm0.2)\cdot10^{17}\frac{\mathrm{W}}{\mathrm{m}^3\hspace{1pt}\mathrm{K}}$ (statistical error). We find that at least up to an absorbed energy density of $124\hspace{2pt}\frac{\mathrm{J}}{\mathrm{cm}^3}$, $G_\mathrm{ep}$ is not fluence-dependent. Our results for the lattice dynamics of platinum provide insights into electron-phonon coupling and phonon thermalization and constitute a basis for quantitative descriptions of platinum-based heterostructures in nonequilibrium conditions.