Diffusion of muonium and hydrogen in diamond

TL;DR

This paper uses quantum transition-state theory with path-integral methods to calculate how vibrational quantization affects impurity diffusion barriers and jump rates of muonium and hydrogen in diamond, aligning well with experimental data.

Contribution

It introduces a quantum approach to evaluate vibrational effects on impurity diffusion barriers in diamond, providing insights beyond classical calculations.

Findings

Effective barriers decrease with temperature for most transitions.

Hydrogen has larger barriers from T to BC sites, muonium the opposite.

Calculated jump rates match experimental muon spin rotation data.

Abstract

Jump rates of muonium and hydrogen in diamond are calculated by quantum transition-state theory, based on the path-integral centroid formalism. This technique allows us to study the influence of vibrational mode quantization on the effective free-energy barriers Delta F for impurity diffusion, which are renormalized respect to the zero-temperature classical calculation. For the transition from a tetrahedral (T) site to a bond-center (BC) position, Delta F is larger for hydrogen than for muonium, and the opposite happens for the transition from BC to T. The calculated effective barriers decrease for rising temperature, except for the muonium transition from T to BC sites. Calculated jump rates are in good agreement to available muon spin rotation data.