Optimum pinning of the vortex lattice in extremely type-II layered superconductors

TL;DR

This study uses Monte Carlo simulations to analyze how pinning affects the vortex lattice in layered type-II superconductors, revealing different phase transitions and the conditions for layer decoupling.

Contribution

It introduces a detailed simulation approach to understand vortex pinning effects and phase transitions in layered superconductors at various pinning strengths.

Findings

Weak pinning leads to 2D melting into a hexatic phase.

Strong pinning induces a Kosterlitz-Thouless transition.

Layer decoupling does not occur at weak pinning below 2D melting.

Abstract

The two-dimensional (2D) vortex lattice in the extreme type-II limit is studied by Monte Carlo simulation of the corresponding 2D Coulomb gas, with identical pins placed at sites coinciding with the zero-temperature triangular vortex lattice. At weak pinning we find evidence for 2D melting into an intermediate hexatic phase. The strong pinning regime shows a Kosterlitz-Thouless transition, driven by interstitial vortex/anti-vortex excitations. A stack of such identical layers with a weak Josephson coupling models a layered superconductor with a triangular arrangement of columnar pins at the matching field. A partial duality analysis finds that layer decoupling of the flux-line lattice does not occur at weak pinning for temperatures below 2D melting.