Hysteresis measurement of anomalous microwave surface resistance in superconducting thin films

The anomalous decrease in microwave surface resistance, R-s, of superconducting YBa2Cu3O7-d (YBCO) thin films in the presence of a low de magnetic field is studied using a microstrip resonator technique. We have done a de field hysteresis measurement of R-s to study the effects of vortex penetration on the anomalous effect. It is shown that the anomaly happens at a field level far below the low critical field, H-c1,H-strip of the superconducting microstrip and that the vortex (Abrikosov) penetration would eliminate the anomalous effect observed at low field. This implies that the anomalous effect does not originate from vortices.