Percolating granular superconductors

TL;DR

This paper studies the critical magnetic fluctuations in percolating granular superconductors using a field-theoretic approach to understand their phase transitions.

Contribution

It introduces a renormalized field theory analysis of diamagnetic susceptibility and magnetic moment fluctuations in a random Josephson network model.

Findings

Determines critical behavior of magnetic susceptibilities at phase transitions.

Analyzes Feynman diagrams to all orders in perturbation theory.

Provides insights into the structure of fluctuations near critical points.

Abstract

We investigate diamagnetic fluctuations in percolating granular superconductors. Granular superconductors are known to have a rich phase diagram including normal, superconducting and spin glass phases. Focusing on the normal-superconducting and the normal-spin glass transition at low temperatures, we study he diamagnetic susceptibility $\chi^{(1)}$ and the mean square fluctuations of the total magnetic moment $\chi^{(2)}$ of large clusters. Our work is based on a random Josephson network model that we analyze with the powerful methods of renormalized field theory. We investigate the structural properties of the Feynman diagrams contributing to the renormalization of $\chi^{(1)}$ and $\chi^{(2)}$. This allows us to determine the critical behavior of $\chi^{(1)}$ and $\chi^{(2)}$ to arbitrary order in perturbation theory.