Microwave Nonlinearities in High Tc Superconductors: The Truth Is Out   There
  This paper discusses some of the major experimental features of microwave nonlinearity in high temperature superconductors, both intrinsic and extrinsic. The case is made for solving the problem of extrinsic nonlinearity through the use of localized measurements of microwave surface impedance and electromagnetic fields. Along these lines, a brief introduction is given to our work on scanning near-field microwave microscopy 
Steven M. Anlage, Wensheng Hu, C. P. Vlahacos, David Steinhauer, B. J.   Feenstra, Sudeep K. Dutta, Ashfaq Thanawalla and F....