Directional pinning and anisotropy in YBa_2Cu_3O_(7-x) with BaZrO_3 nanorods: Intrinsic and nanorods-induced anisotropy

摘要

We present a study of the anisotropic vortex parameters as obtained from measurements of the microwave complex resistivity in the vortex state with a tilted applied magnetic field in YBa_2Cu_3O_(7-x) thin films with BaZrO_3 nanorods. We present the angular dependence of the vortex viscosity η, the pinning constant k_p and the upper limit for the creep factor χ_M. We show that the directional effect of the nanorods is absent in η, which is dictated by the mass anisotropy γ. By contrast, pinning-mediated properties are strongly affected by the nanorods. It is significant that the pinning and creep affected by the nanorods is detectable also at our very high operating frequency, which implies very short-range displacements of the vortices from their equilibrium position.