Probing the nonlinearities arising in the microwave response of superconductors by intermodulation distortion

We present a systematic study of microwave nonlinearity, undertaken on different types of superconductors (Nb, NbN, MgB2 Y-1 beta a(2)Cu(3)O(7-delta)), in thin film form. Experiments are performed in a dielectrically loaded cavity operating at 7 GHz. The dependence of the surface impedance Z(s) and of the third order intermodulation (IMD) products on the power feeding the cavity is analysed, with the aim of shedding a light on the primary mechanisms of nonlinearity. Data from different superconductors are quantitatively compared.