The Surface impedance for various doping of Y_1-xCa _xBa₂Cu₃O_7-δ thin films

The surface impedance for various doping of Y_1-xCa _xBa₂Cu₃O_7-δ thin films was studied at 10GHz using the Parallel Plate resonator. In addition the complex dielectric function was measured using a FIR transmission up to 1THz as a complementary method. The surface resistance was calculated directly from the measured Q factor while the penetration depth variation was obtained from the frequency shift of the resonator. The calculation of the absolute value of the penetration depth used the real part of the dielectric function. All films show a linear temperature dependence of the surface resistance for T < 25K which is consistent with the results obtained for optimally doped single crystals. In the overdoped films the scattering rate shows a steeper decrease by at least one order of magnitude at temperatures below 15K. This is in contrast to a constant value obtained for the optimally doped single crystals and thin films below 20K. In the overdoped films the surface resistance shows a residual value of R_s-res 330μΩ while the optimally doped films show much smaller values of about R_s-res 20μΩ. The overdoped thin films yield a smaller scattering rate than optimally doped single crystals and thin films.