Flux line lattice structure and behaviour in anti-phase boundary free vicinal YBa2Cu3O7-d thin films

TL;DR

This study investigates the flux line lattice structure and behavior in high-quality YBa2Cu3O7-d thin films free of anti-phase boundaries, revealing how the absence of these boundaries influences vortex dynamics and critical current properties.

Contribution

It demonstrates that anti-phase boundary free films exhibit distinct vortex pinning and flux penetration behaviors compared to boundary-rich films, using combined microscopy and magnetic measurements.

Findings

Anti-phase boundary free films show no filamentary flux penetration.

Flux penetration is asymmetric due to intrinsic pinning by tilted a-b planes.

Extended APB free films have different critical current behavior from APB rich films.

Abstract

Field angle dependent critical current, magneto-optical microscopy, and high resolution electron microscopy studies have been performed on YBa2Cu3O7-d thin films grown on mis-cut substrates. High resolution electron microscopy images show that the films studied exhibited clean epitaxial growth with a low density of anti-phase boundaries and stacking faults. Any anti-phase boundaries (APBs) formed near the film substrate interface rapidly healed rather than extending through the thickness of the film. Unlike vicinal films grown on annealed substrates, which contain a high density of anti-phase boundaries, magneto optical imaging showed no filamentary flux penetration in the films studied. The flux penetration is, however, asymmetric. This is associated with intrinsic pinning of flux strings by the tilted a-b planes and the dependence of the pinning force on the angle between the local field and the a-b planes. Field angle dependent critical current measurements exhibited the striking vortex channelling effect previously reported in vicinal films. By combining the results of three complementary characterisation techniques it is shown that extended APB free films exhibit markedly different critical current behaviour as compared to APB rich films. This is attributed to the role of APB sites as strong pinning centres for Josephson string vortices between the a-b planes.