We have carried out non-linear microwave (8 GHz) surface impedance measurements of three YBaCuO thin films in dc magnetic fields Hdc (parallel to c axis) up to 12 mT using a coplanar resonator technique. In zero dc field the three films, deposited by the same method, show a spread of low-power residual surface resistance, Rrcs and penetration depth, A (T = 15 K) within a factor of 1.9. However, they exhibit dramatically different microwave field, Hr; dependences of the surface resistance, Rs, but universal Xs(Hr/) dependence. Application of a dc field was found to affect not only absolute values of R, and Xs, but the functional dependences R,(HTf] and X,(Hr/) as well. For some of the samples the dc field was found to decrease Ra below its zero-field low-power value.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering