Crossing lattices, vortex chains, and angular dependence of melting line in layered superconductors

TL;DR

This paper studies vortex structures and melting transitions in highly anisotropic layered superconductors under tilted magnetic fields, revealing how Josephson vortices and crossing lattices influence melting behavior and vortex arrangements.

Contribution

It introduces a detailed analysis of vortex crossing lattices and their impact on melting lines, explaining experimental observations of vortex chains and lattice states.

Findings

Melting field and temperature depend linearly on in-plane magnetic field.

Small in-plane fields lead to Josephson vortex penetration without tilting the lattice.

Vortex chains form due to stacking of Josephson vortices and pancake strings.

Abstract

We investigate vortex structure and melting transition in very anisotropic layered superconductors at fields tilted with respect to the c-axis. We show that even a small in-plane field does not homogeneously tilt the vortex lattice but, instead, penetrates inside the superconductor in the form of Josephson vortices (JVs) similar to the Meissner state. At high c-axis magnetic field the phase field of the JV is built up from the phase perturbations created by displacements of pancake vortices. The crossing-lattices ground state leads to linear dependencies of the melting field and melting temperature on the in-plane field, in agreement with recent experimental observations. At small fields stacks of JVs accumulate additional pancake strings creating vortex rows with enhanced density. This mechanism explains the mixed chains-lattice state observed by Bitter decorations.