Purely electronic transport and localization in the Bose glass

TL;DR

This paper explores the electronic transport and localization in the Bose glass phase near the superconductor-insulator transition, identifying distinct regimes and predicting activated transport behaviors consistent with experimental observations.

Contribution

It introduces a detailed spectral analysis of the Bose glass phase, revealing three regimes and the existence of a conducting Bose glass with a mobility edge, advancing understanding of disordered bosonic systems.

Findings

Fully localized Bose glass at strongest disorder

Finite-temperature delocalization at weaker disorder

Arrhenius law for conductivity at low temperatures

Abstract

We discuss transport and localization properties on the insulating side of the disorder dominated superconductor-insulator transition, described in terms of the dirty boson model. Analyzing the spectral properties of the interacting bosons in the absence of phonons, we argue that the Bose glass phase admits three distinct regimes. For strongest disorder the boson system is a fully localized, perfect insulator at any temperature. At smaller disorder, only the low temperature phase exhibits perfect insulation while delocalization takes place above a finite temperature. We argue that a third phase must intervene between these perfect insulators and the superconductor. This conducting Bose glass phase is characterized by a mobility edge in the many body spectrum, located at finite energy above the ground state. In this insulating regime purely electronically activated transport occurs, with a conductivity following an Arrhenius law at asymptotically low temperatures, while a tendency to superactivation is predicted at higher T. These predictions are in good agreement with recent transport experiments in highly disordered films of superconducting materials.