MICROWAVE SURFACE IMPEDANCE AT 10 GHZ AND QUASI-PARTICLE SCATTERING IN YBA2CU3O7 FILMS

The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth lambda(T), complex microwave conductivity sigma(T), and quasiparticle scattering rate 1/tau(T) were also determined. After a rapid fall as T is lowered below T(c), the surface resistance R(s) exhibits a linear dependence from 65 K down to 6 K. As T drops below T(c), the real part of the conductivity sigma1 has a rapid rise, which is attributed to the observed dramatic increase in tau. The normal-fluid density shows a linear behavior at low temperatures, which is inconsistent with s-wave BCS superconductivity.