Vortices Clustering: The Origin of the Second Peak in the Magnetisation Loops of High Temperature Superconductors

TL;DR

This paper investigates vortex clustering in high-temperature superconductors and suggests that the second peak in magnetisation loops results from a density-driven vortex instability and clustering phenomena.

Contribution

It introduces a dynamical explanation for the second peak in magnetisation loops, linking vortex clustering to a phase transition in the vortex system.

Findings

Vortex clustering correlates with the second peak in magnetisation.

The instability is associated with a phase transition in the vortex system.

Clustering occurs at regions of the pinning potential.

Abstract

We study vortex clustering in type II Superconductors. We demonstrate that the ``second peak'' observed in magnetisation loops may be a dynamical effect associated with a density driven instability of the vortex system. At the microscopic level the instability shows up as the clustering of individual vortices at (rare) preferential regions of the pinning potential. In the limit of quasi-static ramping the instability is related to a phase transition in the equilibrium vortex system.