We present a new theoretical approach that permits the rf surface impedance ${\mathit{Z}}_{\mathit{s}}$ 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 ${\mathit{Z}}_{\mathit{s}}$ 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.

• Received 25 March 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.386