Angular dependence of the high-frequency vortex response in YBa$_2$Cu$_3$O$_{7-x}$ thin film with self-assembled BaZrO$_3$ nanorods

We present a microwave study of the angular dependence of the flux-flow resistivity $\rho_{ff}$ and of the pinning constant $k_p$ in YBCO thin films containing BZO nanorods. We find that BZO nanorods are very efficient pinning centers, even in tilted fields. We find that $\rho_{ff}$ is a scaling function of a reduced field $H/f(\theta)$. We extend a model for the anisotropic motion of vortices in uniaxially anisotropic superconductor, able to describe the experimental $f(\theta)$ on the basis of only the intrinsic anisotropy of YBCO. The pinning constant $k_p$, by contrast, exhibits different field dependences in different angular ranges, consistent with pinning by BZO at angles as large as 60$^{\circ}$, and with pinning along the $a,b$ planes as originating from the same mechanism as in pure YBCO with the field along the c axis.
Comment: 5 pages, 3 figures