Zero bias anomaly in a two dimensional granular insulator

TL;DR

This study investigates how granularity affects the tunneling density of states in ultrathin silver films, revealing a new regime where individual clusters exhibit metallic behavior despite overall insulating conductivity.

Contribution

It demonstrates that granularity introduces a distinct regime in TDOS, with individual clusters showing metallic properties even in insulating films, contrasting uniform films' behavior.

Findings

Granular films show AA behavior deep in the insulating regime.

Uniform films transition from AA to ES Coulomb gap with disorder.

Granularity creates a regime where clusters are metallic despite overall insulation.

Abstract

We compare tunneling density of states (TDOS) into two ultrathin Ag films, one uniform and one granular, for different degrees of disorder. The uniform film shows a crossover from Altshuler-Aronov (AA) zero bias anomaly to Efros Shklovskii (ES) like Coulomb gap as the disorder is increased. The granular film, on the other hand, exhibits AA behavior even deeply in the insulating regime. We analyze the data and find that granularity introduces a new regime for the TDOS. While the conductivity is dominated by hopping between clusters of grains and is thus insulating, the TDOS probes the properties of an individual cluster which is "metallic".