Superconductor-insulator transition driven by local dephasing

TL;DR

This paper investigates a quantum phase transition from superconducting to insulating states driven by local dephasing effects in a system of bound electron pairs coupled to uncorrelated electrons, using a path-integral approach.

Contribution

It introduces a novel effective action framework for analyzing phase coherence loss in a coupled electron pair system, highlighting the role of local dephasing in the superconductor-insulator transition.

Findings

Transition can be triggered by tuning exchange coupling or bound pair density.

Effective action includes a Berry phase term influencing phase dynamics.

Mechanisms for phase coherence destruction are identified in different coupling regimes.

Abstract

We consider a system where localized bound electron pairs form an array of "Andreev"-like scattering centers and are coupled to a fermionic subsystem of uncorrelated electrons. By means of a path-integral approach, which describes the bound electron pairs within a coherent pseudospin representation, we derive and analyze the effective action for the collective phase modes which arise from the coupling between the two subsystems once the fermionic degrees of freedom are integrated out. This effective action has features of a quantum phase model in the presence of a Berry phase term and exhibits a coupling to a field which describes at the same time the fluctuations of density of the bound pairs and those of the amplitude of the fermion pairs. Due to the competition between the local and the hopping induced non-local phase dynamics it is possible, by tuning the exchange coupling or the density of the bound pairs, to trigger a transition from a phase ordered superconducting to a phase disordered insulating state. We discuss the different mechanisms which control this occurrence and the eventual destruction of phase coherence both in the weak and strong coupling limit.