Vortex Lattice Melting in 2D Superconducting Networks and Films

TL;DR

This study uses Monte Carlo simulations to explore vortex lattice melting in 2D superconducting networks, revealing multiple phase transitions and the nature of vortex matter in different frustration regimes.

Contribution

It provides new insights into vortex lattice melting mechanisms and phase behavior in 2D superconducting networks with different geometries and frustration levels.

Findings

Identified two distinct transitions in dilute systems: depinning and melting.

Found that vortex lattice melting is weakly first order according to KT theory.

Mapped phase diagram including pinned, floating, and liquid vortex phases.

Abstract

We carry out MC studies of 2D superconducting networks, in an applied magnetic field, for square and honeycomb geometries. We consider both dilute systems (f=1/q) and systems near full frustration (f=1/2-1/q). For the dilute case (which models a film as q->infinity), we find two transitions: at T_c(f)~1/q there is a depinning transition from a pinned to a floating vortex lattice; at T_m(f)~constant the floating vortex lattice melts into an isotropic liquid. We analyze this melting according to the Kosterlitz- Thouless theory of dislocation mediated melting, and find that the melting is weakly first order. For the case near full frustration, the system can be described in terms of the density of defects in an otherwise fully frustrated vortex pattern. We find pinned solid, floating solid, and liquid defect phases, as well as a higher sharp transition corresponding to the disordering of the fully frustrated background.