The surface impedance of epitaxial HTSC films in mixed-state

The dependence of surface impedance upon the dc magnetic field is investigated on epitaxial HTSC films. The experimental constants of pinning are about an order of magnitude higher than those following from the critical current of the film. This resulted in an anomalously weak response of the microwave properties of epitaxial HTSC films to the dc magnetic field: the change in the surface resistance of the 1-2-3 film on sapphire in the field of 4 kOe at helium temperatures did not exceed 3%. The temperature dependence of the surface resistance of the mixed-state HTSC film had a maximum near the temperature of the vortex grate depinning. In small dc magnetic field (below 102 Oe), the surface resistance was observed to increase due to intergrain defects