Microwave characterization of laser ablated Y 1Ba 2Cu 3O 7− x thin films

Abstract

In the present study we report the measurements of microwave surface resistance ( R s) of YBCO thin films on LaAlO 3 substrate as a function of temperature, thickness and magnetic field by microstrip resonator technique. The T c( R = 0) of the films is 90 K and J c > 10 6 A/cm 2 at 77 K. The microwave surface resistance has been measured for films of various thicknesses. The value of R s has been found to be initially decreased with increasing film thickness due to increase in number of defects. A minimum microwave surface resistance has been obtained for film thickness of about 300 nm. The increase of R s with film thickness above 300 nm is possibly due to degradation of the film microstructure as observed with Atomic Force Microscopy. Temperature dependence of surface resistance has been studied for best quality films. The field induced variations of surface resistance are also investigated by applying dc magnetic field perpendicular to stripline structure and surface of the film. A general linear and square field dependence of R s at low and high value of fields has been observed with critical field value of 0.4 T which confirms the microwave dissipation induced by flux flow in these resonators at 10 GHz frequency. The hysteresis of R s in dc field observed for field value above critical field shows the higher value of surface resistance in decreasing field than in increasing field which is in agreement with one state critical model and is a characteristic of homogeneous superconductors.