HIGH-FREQUENCY VORTEX DYNAMICS IN YBA2CU3O7

We present a phenomenological description of the high-frequency vortex dynamics in YBa2Cu3O7 and discuss the main parameters related to vort ex motion, namely the viscous drag coefficient eta, the pinning consta nt K-p (Labusch parameter) and the depinning frequency omega(0). We de monstrate experimental results on the angular and temperature dependen ce of eta, K-p and omega(0) in YBa2Cu3O7 and compare these results wit h existing models. We show how studies of the vortex viscosity may yie ld information on the superclean limit. This limit corresponds to the formation of the discrete excitation spectrum in the vortex core due t o quantum confinement and small coherence length. From the low-tempera ture viscosity data we conclude that the superclean limit in YBa2Cu307 is reached for magnetic field perpendicular to the c-axis.