Flux-flow resistivity anisotropy in the instability regime in the a-b plane of epitaxial YBCO thin films

TL;DR

This study investigates the anisotropy of flux-flow resistivity and vortex velocity in YBCO thin films near the instability regime, revealing a consistent 10% higher value along the node direction due to quasiparticle distribution anisotropy.

Contribution

First measurement of flux-flow resistivity and vortex velocity anisotropy in YBCO films near the instability regime along different crystallographic directions.

Findings

Resistivity and vortex velocity are anisotropic, with higher values in the node direction.

Anisotropy is approximately 10% and nearly temperature and field independent.

Results linked to anisotropic quasiparticle distribution on the Fermi surface.

Abstract

Measurements of the nonlinear flux-flow resistivity $\rho$ and the critical vortex velocity $\rm v^*_\phi$ at high voltage bias close to the instability regime predicted by Larkin and Ovchinnikov \cite{LO} are reported along the node and antinode directions of the d-wave order parameter in the \textit{a-b} plane of epitaxial $YBa_2Cu_3O_{7-\delta}$ films. In this pinning-free regime, $\rho$ and $\rm v^*_\phi$ are found to be anisotropic with values in the node direction larger on average by 10% than in the antinode direction. The anisotropy of $\rho$ is almost independent of temperature and field. We attribute the observed results to the anisotropic quasiparticle distribution on the Fermi surface of $YBa_2Cu_3O_{7-\delta}$.