The formation of two-layered YBa₂Cu₃O_{7- delta}superconducting films and their microwave surface resistance

The structure and crystallographic orientation of YBa2Cu3O7- delta films on BaxSr1-xTiO3/MgO heteroepitaxial layers were investigated by the conventional methods of electron diffraction, electron microscopy and by specific methods of Raman scattering of light and backscattering of middle-energy ions. A film of over 350 nm thick may consist of an inner highly-oriented layer and an outer disoriented one. Measurements of the microwave surface resistance Rs at 60 GHz and 4.2 K have confirmed a complicated character of the film structure. It has been shown that the microwave response of two-layer films in a static magnetic field is determined by the losses in the outer disoriented or granular layer and that the dependence Rs(H-) appeals in the field H- starting from approximately 10 Oe.

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