A detailed study was made of the microwave magnetic field dependent surface impedance of a MgB2 thin film, using a parallel plate resonator, as a function of temperature. It was considered whether the framework used to analyze non-linear behavior for other superconductors, both low and high TC, but single-gap, had any validity for MgB2 and whether the films were limited by intrinsic or extrinsic behavior. A key result was the observation of junction-type switching effects at high microwave powers.

Nonlinear Microwave Response of an MgB2 Thin Film. A.J.Purnell, L.F.Cohen, H.Y.Zhai, H.M.Christen, M.P.Paranthaman, D.H.Lowndes, L.Hao, J.C.Gallop: Superconductor Science and Technology, 2004, 17, 681-4