Phase diagram of the vortex system in layered superconductors with strong columnar pinning

TL;DR

This paper investigates the low-temperature phases of vortex systems in layered superconductors with columnar pinning, revealing phase transitions and melting behaviors through numerical free energy minimization.

Contribution

It provides a detailed phase diagram and insights into vortex matter phases, including Bragg glass, Bose glass, and liquid states, with a focus on the effects of pin concentration.

Findings

Confirmation of Bragg glass melting into interstitial liquid via two first-order transitions at low pin concentrations.

Identification of a continuous melting transition at higher pin concentrations characterized by percolation.

Observation of inhomogeneous local melting and depinning crossover phenomena.

Abstract

We present the results of a detailed investigation of the low-temperature properties of the vortex system in strongly anisotropic layered superconductors with a random array of columnar pinning centers. Our method involves numerical minimization of a free energy functional in terms of the time-averaged local vortex density. It yields the detailed vortex density distribution for all local free-energy minima, and therefore allows the computation of any desired correlation function of the time-averaged local vortex density. Results for the phase diagram in the temperature vs. pin concentration plane at constant magnetic induction are presented. We confirm that for very low pin concentrations, the low-temperature phase is a Bragg glass, which melts into an interstitial liquid phase via two first-order steps, separated by a Bose glass phase. At higher concentrations, however, the low-temperature phase is a Bose glass, and the melting transition becomes continuous. The transition is then characterized by the onset of percolation of liquid-like regions across the sample. Inhomogeneous local melting of the Bose glass is found to occur. There is also a depinning crossover between the interstitial liquid and a completely unpinned liquid at higher temperatures. At sufficiently large pin concentrations, the depinning line merges with the Bose glass to interstitial liquid transition. Many of the features we find have been observed experimentally and in simulations. We discuss the implications of our results for future experimental and theoretical work.