Resistive transition in disordered superconductors with varying intergrain coupling

TL;DR

This paper investigates how varying intergrain coupling affects the resistive transition in disordered granular superconductors, revealing different transition behaviors and broadening effects with increasing disorder, using numerical simulations and effective medium theory.

Contribution

It models disordered superconductors as Josephson junction networks to analyze the impact of intergrain coupling strength on resistive transitions, providing new insights into superconductivity in disordered systems.

Findings

Resistive transition occurs at lower temperatures with increased disorder.

Strong links enhance broadening of the transition curve.

Different behaviors are observed between weak and strong link systems.

Abstract

The effect of disorder is investigated in granular superconductive materials with strong and weak links. The transition is controlled by the interplay of the \emph{tunneling} $g$ and \emph{intragrain} $g_{intr}$ conductances, which depend on the strength of the intergrain coupling. For $g \ll g_{intr}$, the transition involves first the grain boundary, while for $g \sim g_{intr}$ the transition occurs into the whole grain. The different intergrain coupling is considered by modelling the superconducting material as a disordered network of Josephson junctions. Numerical simulations show that on increasing the disorder, the resistive transition occurs for lower temperatures and the curve broadens. These features are enhanced in disordered superconductors with strong links. The different behaviour is further checked by estimating the average network resistance for weak and strong links in the framework of the effective medium approximation theory. These results may be relevant to shed light on long standing puzzles as: (i) enhancement of the superconducting transition temperature of many metals in the granular states; (ii) suppression of superconductivity in homogeneously disordered films compared to standard granular systems close to the metal-insulator transition; (iii) enhanced degradation of superconductivity by doping and impurities in strongly linked materials, such as magnesium diboride, compared to weakly-linked superconductors, such as cuprates.