Overview of Nonlinearity in HTS: What Learned and Prospects for Improvement

The linear surface resistance of the HTS materials is low enough to support a variety of applications that can surpass conventional technology. However, nonlinearity in the form of intermodulation distortion (IMD) is a serious limiting effect for some applications. The nonlinear effects are only weakly correlated with the low-power surface impedance, and considerable material variation has been the hallmark of IMD. With improvement in film quality, the intrinsic nonlinearity now seems to be the most important source of IMD. Presented here is a brief review of the experimental situation and a comparison with the theories of intrinsic nonlinearity. Suggestions for further work are given.