Electronic stopping power in gold: The role of d electrons and the H/He anomaly

TL;DR

This study uses advanced density-functional theory to accurately analyze how hydrogen and helium ions lose energy in gold, revealing the roles of d electrons and explaining previously puzzling experimental anomalies.

Contribution

It provides the first high-accuracy first-principles explanation of electronic stopping power in gold, including the d-electron involvement and the H/He anomaly.

Findings

Reproduced the non-linear stopping power versus velocity behavior.

Explained the H/He anomaly through d-electron screening.

Demonstrated the importance of d electrons at low velocities.

Abstract

The electronic stopping power of H and He moving through gold is obtained to high accuracy using time-evolving density-functional theory, thereby bringing usual first-principles accuracies into this kind of strongly coupled, continuum non-adiabatic processes in condensed matter. The two key unexplained features of what observed experimentally have been reproduced and understood: (i) The non-linear behaviour of stopping power versus velocity is a gradual crossover as excitations tail into the d-electron spectrum; and (ii) the low-velocity H/He anomaly (the relative stopping powers are contrary to established theory) is explained by the substantial involvement of the d electrons in the screening of the projectile even at the lowest velocities where the energy loss is generated by s-like electron-hole pair formation only.