Nonlinear Response of HTSC Thin Film Microwave Resonators in an Applied   DC Magnetic Field
  The non-linear microwave surface impedance of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field of magnitude comparable to that of the microwave field. Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied DC field before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance. 
Durga P. Choudhury, Balam A. Willemsen, John S. Derov and S. Sridhar   (Physics Department, Northeastern University and Rome...