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

摘要

Measurements of the nonlinear flux-flow resistivity $\rho$ and the criticalvortex velocity $\rm v^*_\phi$ at high voltage bias close to the instabilityregime predicted by Larkin and Ovchinnikov \cite{LO} are reported along thenode 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 nodedirection larger on average by 10% than in the antinode direction. Theanisotropy of $\rho$ is almost independent of temperature and field. Weattribute the observed results to the anisotropic quasiparticle distribution onthe Fermi surface of $YBa_2Cu_3O_{7-\delta}$.