Microwave dissipation in single-crystal high-T_c superconductors

We report here detailed microwave-absorption studies on single crystals of both Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O systems. A linear ohmic response is found at microwave frequencies, with the absorbed power proportional to the incident microwave power. The dependence of the signal on the angle between the applied dc field and the c axis shows that the absorption scales with the magnetic component along the c axis. A broad maximum is observed in the derivative signal of the absorbed power as the applied field B is varied at constant temperature. The peak field thus defined shows B∝(1-T/T_c)^3/2 dependence on temperature. The scaling of the data at different T and B gives a universal function for resistivity as ρ=F[B/(1-T/T_c)^3/2]. Inconsistency with the Kosterlitz-Thouless transition is also discussed.