  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.
