Nonlinearity in the microwave properties of MgB2 thin films: power dependence and intermodulation distortion

We present here measurements carried out by using a dielectrically loaded copper cavity operating at 7 GHz on MgB₂ thin films synthesized by hybrid physical-chemical vapor deposition. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio between 15 and 17, are presented. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity is analyzed, with the aim of shedding a light on the primary dissipation mechanisms. At low power, data from both power dependence and third order products seem to indicate that we are observing a nonlinear response which is inherent to the conventional s-wave nature of this novel compound. At intermediate-to-high circulating power values, vortex penetration appears to be the limiting mechanism for the power handling capability of MgB₂ films.