THEORY OF RF MAGNETIC-PERMEABILITY OF ISOTROPIC TYPE-II SUPERCONDUCTORS IN A PARALLEL FIELD

A theoretical description of the complex rf magnetic permeability mu approximately = mu' + i-mu" of isotropic type-II superconductors in a parallel applied static magnetic field is presented. The results are based upon a self-consistent treatment of vortex dynamics which simultaneously includes the effects of pinning, flux flow, and flux creep, together with nonlocal vortex interactions. The results are expected to be valid over a wide range of frequencies, magnetic inductions, and temperatures. We show how a mu"-peak line, closely related to the irreversibility line, arises from the theoretical result for the permeability as a function of temperature, magnetic field, and frequency. This theory opens the possibility of investigating flux creep and depinning at frequencies into the GHz range.