Anomalous thermal activation of the electron glass dynamics in a-InOx and granular aluminum

TL;DR

This study reveals that the electron glass dynamics in amorphous indium oxide and granular aluminum are thermally activated, with an unusual temperature-dependent activation energy increasing as T^2, challenging previous beliefs and advancing understanding of electron glasses.

Contribution

It demonstrates thermal activation of electron glass dynamics in a-InOx, contradicting prior assumptions, and uncovers an anomalous T^2 dependence of activation energy in these systems.

Findings

Electron glass dynamics in a-InOx slow down with cooling and speed up with heating.

Thermal activation observed in both a-InOx and granular Al systems.

Activation energy increases with temperature as T^2, an unexplained phenomenon.

Abstract

In this article, we explore the temperature dependence of the electrical glassy dynamics in insulating amorphous indium oxide (a-InOx) and granular Al films. We use non-isothermal gate voltage protocols, which can reveal changes in the dynamics induced by the temperature, when logarithmic relaxations devoid of characteristic times are at work. We demonstrate that, contrary to almost 20 years of opposite belief, the dynamics of amorphous indium oxide films in the liquid helium temperature range is thermally activated, i.e. it slows down under cooling and accelerates upon heating. Amorphous indium oxide thus adds to the list of glassy disordered systems in which we already demonstrated thermal activation, which includes granular Al and amorphous NbxSi1-x films. Moreover, measurements up to 40 K in a-InOx and granular Al films reveal the close similarity between the two systems and a very anomalous character of the thermal activation, with an effective activation energy increasing with T as T^2 . We so far have no explanation for it. Its further study and understanding may be important for the physics of electron glasses.