Grain boundaries in vortex matter

TL;DR

This paper investigates the properties of grain boundaries in vortex matter within type II superconductors, revealing their impact on pinning, transport, and potential phase transitions, supported by theoretical and numerical analysis.

Contribution

It introduces a model treating grain boundaries as dislocation arrays with non-local surface tension, highlighting their influence on superconductor properties and vortex lattice melting.

Findings

Grain boundaries are less rough than isolated dislocations.

Critical current is higher in vortex polycrystals than in regular lattices.

Melting may occur via an intermediate polycrystalline phase.

Abstract

We explore the statistical properties of grain boundaries in the vortex polycrystalline phase of type II superconductors. Treating grain boundaries as arrays of dislocations interacting through linear elasticity, we show that self-interaction of a deformed grain boundary is equivalent to a non-local long-range surface tension. This affects the pinning properties of grain boundaries, that are found to be less rough than isolated dislocations. The presence of grain boundaries has an important effect on the transport properties of type II superconductors as we show by numerical simulations: our results indicate that the critical current is higher for a vortex polycrystal than for a regular vortex lattice. Finally, we discuss the possible role of grain boundaries in vortex lattice melting. Through a phenomenological theory we show that melting can be preceded by an intermediate polycrystalline phase.