Melting a granular glass by cooling

TL;DR

This paper demonstrates through simulations that reducing driving amplitude can melt a granular glass into a fluid, highlighting friction's role in facilitating particle escape from cages, contrary to usual expectations.

Contribution

It reveals a re-entrance melting transition in driven granular glasses induced by lowering the driving amplitude, emphasizing the impact of frictional interactions on particle dynamics.

Findings

Re-entrance melting transition observed with decreased driving amplitude.

Super-diffusive particle behavior during the transition.

Frictional interactions enable particles to escape cages.

Abstract

Driven granular systems readily form glassy phases at high particle volume fractions and low driving amplitudes. We use computer simulations of a driven granular glass to evidence a re-entrance melting transition into a fluid state, which, contrary to intuition, occurs by \emph{reducing} the amplitude of the driving. This transition is accompanied by anomalous particle dynamics and super-diffusive behavior on intermediate time-scales. We highlight the special role played by frictional interactions, which help particles to escape their glassy cages. Such an effect is in striking contrast to what friction is expected to do: reduce particle mobility by making them stick.