Nonlinear Microwave Properties of High-Temperature Superconducting YBa2Cu3O7-δ Single Crystal Thin Films

This work establishes the possible sources of nonlinear microwave response in perfect epitaxially-grown single-crystal HTS YBa
₂
Cu
₃
O
_7-δ
(YBCO) thin films, their origin and conditions at which they become essential, as well as possibilities for their mitigation. Microwave measurements of YBCO thin film coplanar and strip-line resonators are performed at different experimental conditions. The nonlinear surface resistance of these resonators are studied as a function of the rf current amplitude at different temperatures and dc magnetic field for field-cooled experiments.