Absence of Quantum Metallic Behavior in Disordered Granular Superconductors

TL;DR

This paper investigates the behavior of disordered granular superconductors, challenging the idea that a finite resistivity at zero temperature indicates metallic behavior, and explores the roles of phase glass and vortex-glass transitions.

Contribution

It clarifies the interplay between phase glass and superconducting fluctuations, showing that resistivity drops are linked to vortex-glass ordering rather than metallicity.

Findings

Coupling between phase glass order and SC fluctuations leads to divergent conductivity.

Resistivity drops are associated with vortex-glass transition, not metallic behavior.

Absence of true quantum metallic state in disordered granular superconductors.

Abstract

We examine the idea, postulated by Phillips et al., that a finite resistivity in $T \to 0$ limit in disordered granular superconducting (SC) films is explained as a consequence of the absence of phase stiffness in a phase glass (PG) peculiar to granular systems. It is found that a coupling between the nonzero PG order and the ordinary SC fluctuation makes the conductivity divergent. However, an actual drop of resistivity is argued to occur due to another SC glass ordering, induced by the precursory PG fluctuation, corresponding to the vortex-glass transition in a nonzero magnetic field.