Short Range Order-Long Range Order in Superconducting Materials.
Final scientific rept. 1 Oct 80-30 Sep 84,
WISCONSIN UNIV-MILWAUKEE DEPT OF PHYSICS
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Surface waves propagating through NbN films which are columnar in nature and which therefore may behave like inhomogeneous two dimensional superconductors with localized electronic states show attenuation curves which yield an effective superconducting energy gap which saturates at about one third the usual value. A model has been proposed that ascribes this order parameter reduction to the localization of electronic states in the columnar regions. The piezoelectrically induced attenuation curve in a superconducting NbN film is shifted by almost 5 K below the resistivity curve of the film. This shift may be attributed to the resistance in the cores of the Kosterlitz-Thouless vortex-antivortex flux pairs which may exist in an inhomogeneous superconductor. A superconducting granular lead film has been investigated with surface acoustic waves propagating on the piezoelectric substrate. Most of the piezoelectrically induced attenuation in the normal state is quenched when the film becomes superconducting. The residual attenuation that remains in the superconducting state may be related to the fact that the surface acoustic wave samples the sheet resistivity of a small number of granules.
- Electricity and Magnetism