New insight into the diffusion of hydrogen and helium atoms in tungsten

TL;DR

This paper reveals that hydrogen and helium atoms diffuse in tungsten through non-Markovian jumps with power-law waiting times, leading to ergodicity-breaking behavior, which challenges traditional diffusion models and enhances understanding of their experimental behaviors.

Contribution

It introduces a novel view of H/He diffusion in tungsten, showing non-Markovian jump processes with power-law waiting times, impacting future theoretical and experimental studies.

Findings

Diffusion involves non-Markovian jumps with power-law waiting times.

Waiting time distribution is temperature-dependent and non-exponential.

Diffusion exhibits ergodicity-breaking behavior.

Abstract

Based on the in-detail tracking of the movements of atoms in a large number of molecular dynamics simulation boxes, we find that the diffusion of H and He atoms in single-crystal W is composed of non-Markovian jumps. The waiting time distribution of the triggering of jumps is not the usually recognized exponential distribution, but a temperature-dependent power-law distribution. The power-law distribution of the waiting time may lead to clear ergodicity-breaking diffusion, a phenomenon that has formerly been reported to only occur in complex systems such as living biological cells or soft matter. The present finding provides an insightful new view for the analysis and simulation of the puzzling H/He behaviors in W that are observed in experiments. Our findings will inspire reconsiderations on how to bridge the multiscale theoretical predictions with experimental observations, not only for H/He in W but also for H/He in other materials.