Field-induced superdiffusion and dynamical heterogeneity

TL;DR

This paper links field-induced superdiffusion in supercooled liquids to dynamical heterogeneity, showing that anomalous transport arises from localized mobile regions affecting probe dynamics, supported by simulations and analytical insights.

Contribution

It demonstrates that superdiffusion and Stokes-Einstein violation are caused by dynamical heterogeneity, providing a unified physical explanation through models and analysis.

Findings

Superdiffusion scales as t^{3/2} under pulling force.

Violation of the Stokes-Einstein relation is linked to heterogeneous dynamics.

Population splitting into mobile and immobile groups explains anomalous fluctuations.

Abstract

By analyzing two Kinetically Constrained Models of supercooled liquids we show that the anomalous transport of a driven tracer observed in supercooled liquids is another facet of the phenomenon of dynamical heterogeneity. We focus on the Fredrickson-Andersen and the Bertin-Bouchaud-Lequeux models. By numerical simulations and analytical arguments we demonstrate that the violation of the Stokes-Einstein relation and the observed field-induced superdiffusion have the same physical origin: while a fraction of probes do not move, others jump repeatedly because they are close to local mobile regions. The anomalous fluctuations observed out of equilibrium in presence of a pulling force $\epsilon$, $\sigma_x^2(t) = \langle x_\epsilon^2(t) \rangle - \langle x_\epsilon(t) \rangle^2 \sim t^{3/2}$, which are accompanied by the asymptotic decay $\alpha_\epsilon(t)\sim t^{-1/2}$ of the non-Gaussian parameter from non-trivial values to zero, are due to the splitting of the probes population in the two (mobile and immobile) groups and to dynamical correlations, a mechanism expected to happen generically in supercooled liquids.