Strong quantum interference in strongly disordered bosonic insulators

TL;DR

This paper investigates quantum interference effects in disordered bosonic insulators, revealing how magnetic fields influence conductivity and induce a transition from Mott's law to activation behavior.

Contribution

It introduces a functional renormalization group method to analyze bosonic VRH with strong quantum interference, providing new insights into magnetic field effects.

Findings

Large positive magnetoresistance observed.

Conductivity crossover from Mott's law to activation behavior.

Activation gap proportional to magnetic field.

Abstract

We study the variable-range hopping (VRH) of bosons in an array of sites with short-range interactions and a large characteristic coordination number. The latter leads to strong quantum interference phenomena yet allows for their analytical study. We develop a functional renormalization group scheme that repeatedly eliminates high-energy sites properly renormalizing the tunnelling between the low-energy ones. Using this approach we determine the temperature and magnetic field dependence of the hopping conductivity and find a large positive magnetoresistance. With increasing magnetic field the behaviour of the conductivity crossovers from the Mott's law to an activational behaviour with the activation gap proportional to the magnetic field.