Decoupling and Depinning II: Flux lattices in disordered layered superconductors

TL;DR

This paper investigates phase transitions in flux lattices within disordered layered superconductors, revealing the emergence of a Josephson glass phase, layer decoupling, and complex transition lines influenced by disorder and thermal fluctuations.

Contribution

It introduces a detailed phase diagram for flux lattices in disordered layered superconductors, identifying a Josephson glass phase and the interplay of depinning and decoupling transitions.

Findings

Disorder induces a Josephson glass phase at low temperatures.

Depinning transition is marked by the vanishing of JG order.

Layer decoupling occurs due to disorder and thermal fluctuations.

Abstract

Phase transitions of a flux lattice in layered superconductors with magnetic field perpendicular to the layers and in presence of disorder are studied. We find that disorder generates a random Josephson coupling between layers which leads to a Josephson glass (JG) phase at low temperatures; vanishing of the JG order identifies a depinning transition. We also find that disorder and thermal fluctuations lead to layer decoupling where the renormalized Josephson coupling vanishes. Near decoupling an anharmonic regime is found, where usual elasticity and the resulting Bragg glass are not valid. The depinning line crosses the decoupling line at a multicritical point, resulting in three transition lines and a crossover line. The phase diagram is consistent with the unusual data on Bi2Sr2CaCu2O8 such as the "second peak" and depinning transitions. The Josephson plasma frequency is evaluated in the various phases.