Anomalies in Nonlinear Microwave Surface Impedance of YBCO Thin Films on MgO: Superconductor Versus Substrate Effects
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Colleges, School and Institutes
The nonlinear microwave surface impedances Z(s) = R-s + jX(s) of three epitaxial YBa2Cu3O7-delta (YBCO) thin films deposited by thermal co-evaporation on MgO substrates have been, studied by the coplanar resonator technique at 8 GHz in the temperature T range 12 to 60-K in both zero and finite (similar to10 mT) DC magnetic fields. All the films exhibited an anomalous decrease in the. sur face resistance. R. as a function of microwave magnetic field H-rf below 20 K. In one of the films, the application of a DC. field of 10 mT has also induced an anomalous decrease in the penetration depth lambda (H-rf). Analysis of the results suggests that the anomalies may be originating both in the film and in the substrate, and ways to distinguish between the two contributions are proposed. The consequences of the observed phenomena for application of YBCO films in microwave devices are discussed.
|Number of pages||4|
|Journal||IEEE Transactions on Applied Superconductivity|
|Publication status||Published - 1 Jun 2003|
- microwave nonlinearity, DC magnetic field, anomalous response, high temperature superconductor