Anomalies in the electronic stopping of slow antiprotons in LiF

TL;DR

This paper presents first-principles calculations revealing the Barkas effect in the electronic stopping power of protons and anti-protons in LiF, clarifying previous conflicting predictions and showing stopping power vanishes at very low velocities.

Contribution

The study provides the first-principles confirmation of the Barkas effect in LiF and explains discrepancies with prior predictions by analyzing trajectory effects.

Findings

Barkas effect observed: higher stopping for protons than anti-protons.

Previous anti-Barkas prediction attributed to symmetric trajectories.

Stopping power vanishes below 0.1 a.u. velocity.

Abstract

We present first-principles theoretical calculations for the electronic stopping power (SP) of both protons and anti-protons in LiF. Our results show the presence of the Barkas effect: a higher stopping for positively charged particles than their negatively charged antiparticles. In contrast, a previous study has predicted an anti-Barkas effect (higher stopping for negative charges) at low velocity [Qi, Bruneval and Maliyov, Phys. Rev. Lett. 128, 043401 (2022)]. We explain this discrepancy by showing that this anti-Barkas effect appears for highly symmetric trajectories and disappears when considering trajectories that better reproduce the experimental setup. Our low-velocity results show that the SP of both protons and anti-proton vanish for velocities under 0.1 a.u. .