VORTEX-MOTION DISSIPATION IN HIGH-TC SUPERCONDUCTORS AT MICROWAVE-FREQUENCIES

Measurements of the microwave surface resistance on samples of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O at different frequencies (23 and 48 GHz) indicate a universal behavior of the dissipation due to the vortex motion as a function of temperature, at low magnetic field. A temperature T0 = (0.97 +/- 0.01)T(c) separates two regimes such that for T < T0 the dissipation increases with T while, for T0 < T < T(c) the dissipation decreases with increasing T. The role of fluctuations is expedient for explaining the experimental data near T(c).