Slow Conductance Relaxation in Insulating Granular Al: Evidence for Screening Effects

TL;DR

This paper investigates conductance relaxation in insulating granular aluminum films, revealing a finite screening length of about 10nm at 4K, which impacts electron glass models of disordered insulators.

Contribution

It provides evidence for a finite screening length in insulating granular Al films and highlights its importance in understanding conductance relaxation.

Findings

Conductance relaxations consist of two contributions: gate-sensitive and gate-independent.

Screening length in insulating granular Al is approximately 10nm at 4K.

Metallic-like screening effects influence electron glass behavior in disordered insulators.

Abstract

It is shown that the conductance relaxations observed in electrical field effect measurements on granular Al films are the sum of two contributions. One is sensitive to gate voltage changes and gives the already reported anomalous electrical field effect. The other one is independent of the gate voltage history and starts when the films are cooled down to low temperature. Their relative amplitude is strongly thickness dependent which demonstrates the existence of a finite screening length in our insulating films and allows its quantitative estimate (about 10nm at 4K). This metallic-like screening should be taken into account in the electron glass models of disordered insulators.