Growth of CaF2 buffer on Si using low energy cluster beam deposition technique and study of its properties

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Peak-effect, a new phenomenon observed at microwave frequencies in high Tc superconductor thin films

Measurements of microwave surface resistance in magnetic fields (parallel to c-axis), ranging between 0.2 and 0.9 T, of high quality epitaxial DyBa2Cu3O7-y and YBa2Cu3O7-y superconducting thin films show a pronounced peak near the superconducting transition temperature. It is more pronounced at a frequency of 9.55 GHz as compared to 4.88 GHz. The exact nature of the peak is somewhat sample-dependent thereby indicating that the nature and distribution of defects in the films or the pinning sites determine the nature of the peaks; however, it follows the general trend that as the magnetic field is increased the peak shifts towards the lower temperature and is absent when the field is zero. The temperature and field dependence of the peak suggests that this peak could be associated with the order–disorder transition of the flux-line lattice. The peak-effect shows strong frequency dependence close to the depinning frequency of the flux line lattice. We explain our data in terms of the temperature dependence of the Labusch parameter within the collective pinning scenario in type II superconductors.

Peak effect in surface resistance at microwave frequencies in Dy-123 thin films

A pronounced peak in the microwave (at frequency 9.55 GHz) surface resistance, Rs vs. T plot (where T is the temperature) has been observed in epitaxial DyBa2Cu3O7−y superconducting thin films in magnetic fields (parallel to c-axis) in the range 2 to 8 kOe, and temperatures close to the superconducting transition temperature Tc(H). Our data suggest that the nature of peaks observed in the two films is different, thereby indicating different defect structures in the films.