Non-linear Microwave Surface Impedance of Epitaxial HTS Thin Films in Low DC Magnetic Fields

A. P. Kharel; K. H. Soon; J. R. Powell; A. Porch; M. J. Lancaster; A. V. Velichko; R. G. Humphreys

doi:10.1109/77.784886

paper

Non-linear Microwave Surface Impedance of Epitaxial HTS Thin Films in Low DC Magnetic Fields

arXiv:cond-mat/9903309 · doi:10.1109/77.784886

Abstract

We have carried out non-linear microwave (8 GHz) surface impedance measurements of three YBaCuO thin films in dc magnetic fields $H_{d c}$ (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, $R_{r es}$ and penetration depth, $λ$ (T=15 K) within a factor of 1.9. However, they exhibit dramatically different microwave field, $H_{r f}$ dependences of the surface resistance, $R_{s}$ , but universal $X_{s} (H_{r f})$ dependence. Application of a dc field was found to affect not only absolute values of $R_{s}$ and $X_{s}$ , but the functional dependences $R_{s} (H_{r f})$ and $X_{s} (H_{r f})$ as well. For some of the samples the dc field was found to decrease $R_{s}$ below its zero-field low-power value.

4 pages, 4 figures. To be published in IEEE Trans. Appl. Supercond., June 1999