Joule heating and high frequency nonlinear effects in the surface impedance of high Tc superconductors

Using the dielectric resonator method, we have investigated nonlinearities in the surface impedance Z(s)=R-s+jX(s) of YBa2Cu3O7-delta thin films at 10 GHz as a function of the incident microwave power level and temperature. The use of a rutile dielectric resonator allows us to measure the precise temperature of the films. We conclusively show that the usually observed increase in the surface resistance of YBa2Cu3O7-delta thin film as a function of microwave power is due to local heating. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3079520]