Manifestation of ageing in the low temperature conductance of disordered insulators

TL;DR

This study investigates ageing phenomena in the low-temperature conductance of disordered insulators, providing evidence that their dynamics depend on age and are related by a superposition principle, shedding light on glassy electronic states.

Contribution

It presents new measurements on granular aluminium films demonstrating age-dependent conductance dynamics and clarifies the interpretation of relaxation protocols in disordered insulators.

Findings

Conductance dynamics depend on the age of the sample.

Different relaxation protocols are related by a superposition principle.

Results support the presence of a glassy electron state.

Abstract

We are interested in the out of equilibrium phenomena observed in the electrical conductance of disordered insulators at low temperature, which may be signatures of the electron coulomb glass state. The present work is devoted to the occurrence of ageing, a benchmark phenomenon for the glassy state. It is the fact that the dynamical properties of a glass depend on its age, i.e. on the time elapsed since it was quench-cooled. We first critically analyse previous studies on disordered insulators and question their interpretation in terms of ageing. We then present new measurements on insulating granular aluminium thin films which demonstrate that the dynamics is indeed age dependent. We also show that the results of different relaxation protocols are related by a superposition principle. The implications of our findings for the mechanism of the conductance slow relaxations are then discussed.