Title: Analysis of the measurements of anisotropic a.c. vortex resistivity in tilted magnetic fields,
Abstract: Measurements of the high-frequency complex resistivity in superconductors are
a tool often used to obtain the vortex parameters, such as the vortex
viscosity, the pinning constant and the depinning frequency. In anisotropic
superconductors, the extraction of these quantities from the measurements faces
new difficulties due to the tensor nature of the electromagnetic problem. The
problem is specifically intricate when the magnetic field is tilted with
respect to the crystallographic axes. Partial solutions exist in the
free-flux-flow (no pinning) and Campbell (pinning dominated) regimes. In this
paper we develop a full tensor model for the vortex motion complex resistivity,
including flux-flow, pinning, and creep. We give explicit expressions for the
tensors involved. We obtain that, despite the complexity of the physics, some
parameters remain scalar in nature. We show that under specific circumstances
the directly measured quantities do not reflect the true vortex parameters, and
we give procedures to derive the true vortex parameters from measurements taken
with arbitrary field orientations. Finally, we discuss the applicability of the
angular scaling properties to the measured and transformed vortex parameters
and we exploit these properties as a tool to unveil the existence of
directional pinning.