Abstract
We present a new theoretical approach that permits the rf surface impedance Zs of type-II superconductors to be calculated over a wide range of angular frequencies ω, magnetic inductions B, and temperatures T. Our approach, based on a self-consistent treatment of vortex dynamics, includes the influence of both vortex pinning and flux creep upon Zs in a unified manner, by making use of continued-fraction-expansion results for the dynamic mobility of a particle undergoing Brownian motion in a periodic potential.