Superconducting transition in disordered granular superconductors in magnetic fields

TL;DR

This paper investigates the superconducting transition in disordered granular superconductors under magnetic fields, revealing that in 3D systems the transition can occur above the conventional upper critical field due to quantum fluctuations.

Contribution

It demonstrates that the glass transition in granular superconductors can be understood similarly to vortex-glass transitions in amorphous materials, incorporating superconducting fluctuations.

Findings

Resistivity vanishes above $H_{c2}(0)$ in 3D granular systems.

Sharp resistivity drops in 2D occur below $H_{c2}$ due to quantum fluctuations.

Glass transition curves in granular materials align with vortex-glass transition theory.

Abstract

Motivated by a recent argument that the superconducting (SC) transition field of three-dimensional (3D) disordered superconductors with granular structure in a nonzero magnetic field should lie above $H_{c2}(0)$ in low $T$ limit, the glass transition (or, in 2D, crossover) curve $H_g(T)$ of disordered quantum Josephson junction arrays is examined by incorporating SC fluctuations. It is found that the glass transition or crossover in the granular materials can be described on the same footing as the vortex-glass (VG) transition in amorphous-like (i.e., nongranular) materials. In most of 3D granular systems, the vanishing of resistivity upon cooling should occur even above $H_{c2}(0)$, while the corresponding sharp drop of the resistivity in 2D case may appear only below $H_{c2}$ as a result of an enhanced quantum fluctuation.