Peak effect due to competing vortex ground states in superconductors with large inclusions

TL;DR

This paper explores how large inclusions in superconductors affect vortex pinning and critical currents, revealing a series of phase transitions and peaks in the field dependence of the critical current due to vortex-inclusion interactions.

Contribution

It introduces a detailed simulation study of vortex interactions with large defects, uncovering first-order phase transitions and their impact on critical current behavior.

Findings

Pin-breaking force depends on inclusion size and anisotropy.

Series of first-order phase transitions occur at specific magnetic fields.

Critical current exhibits peaks between vortex occupation transition points.

Abstract

Superconductors can support large dissipation-free electrical currents only if vortex lines are effectively immobilized by material defects. Macroscopic critical currents depend on elemental interactions of vortices with individual pinning centers. Pinning mechanisms are nontrivial for large-size defects such as self-assembled nanoparticles. We investigate the problem of a vortex system interacting with an isolated defect using time-dependent Ginzburg-Landau simulations. In particular, we study the instability-limited depinning process and extract the dependence of the pin-breaking force on inclusion size and anisotropy for an \emph{isolated vortex line}. In the case of a \emph{vortex lattice} interacting with a large isolated defect, we find a series of first-order phase transitions at well-defined magnetic fields, when the number of vortex lines occupying the inclusion changes. The pin-breaking force has sharp local minima at those fields. As a consequence, in the case of isolated identical large-size defects, the field dependence of the critical current is composed of a series of peaks located in between the occupation-number transition points.