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High temperature superconductivity

Several promising deposition techniques and structural and electromagnetic characterization methods have been used to improve the microstructure and reduce the microwave losses of YBa2Cu3O7-X films.

YBa2Cu3O7-X films of high structural quality have been epitaxially grown on single crystalline magnesium oxide and/or lanthanum aluminium oxide substrates using 4 deposition techniques. Transition temperatures between 85 K and 92 K, transition width of less than 1K, and critical current densities above 10E6 A/cm2 at 77K have been measured inductively.
The surface impedance of these films has been measured at 87 GHz and 19 GHz. While there is only little scatter of the data for the surface resistance around 60 K and the penetration depth, the residual losses depend strongly on the oxygen content and order in the copper oxide chains and weakly on the cation stoichiometry.

The magnetic properties and the harmonic generation in field modulated microwave absorption of selected films have been studied comparatively. The magnetoresistance, the irreversibility line and the harmonic generation depend on the film quality and thickness. Coplanar resonators have been patterned by photolithography from some of these films. Quality factors in excess of 40000 at 15 K and 8 GHz up to microwave fields of 10E4 A/m have been achieved in the best case. However, at high fields there is a much stronger dependence on the film quality than at low fields.

Reported by

Bergische Universitaet Gesamthochschule Wuppertal
Gausstrasse 20 Postfach 10 01 27
42119 Wuppertal
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