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, MgB
₂
, Y
₁
Ba
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.