Negative differential mobility of weakly driven particles in models of glass formers

TL;DR

This paper investigates how probe particles in glassy systems respond to weak forces, revealing non-monotonic behavior like negative differential mobility and giant diffusivity due to dynamic heterogeneity.

Contribution

It demonstrates the occurrence of negative differential mobility and giant diffusivity in kinetically constrained models of glass formers, with analytical explanations based on continuous-time random walks.

Findings

Probe response can be non-monotonic under weak driving forces.

Dynamic heterogeneity causes decoupling of persistence and exchange times.

Bimodal displacement distributions are observed in the system.

Abstract

We study the response of probe particles to weak constant driving in kinetically constrained models of glassy systems, and show that the probe's response can be non-monotonic and give rise to negative differential mobility: increasing the applied force can reduce the probe's drift velocity in the force direction. Oth er significant non-linear effects are also demonstrated, such as the enhancement with increasing force of the probe's fluctuations away from the average path, a phenomenon known in other contexts as giant diffusivity. We show that these res ults can be explained analytically by a continuous-time random walk approximatio n where there is decoupling between persistence and exchange times for local dis placements of the probe. This decoupling is due to dynamic heterogeneity in the glassy system, which also leads to bimodal distributions of probe particle disp lacements. We discuss the relevance of our results to experiments.