THE SURFACE IMPEDANCE OF EPITAXIAL HTSC F ILMS IN MIXED-STATE

The dependence of surface impedance upon the dc magnetic field is inve stigated on epitaxial HTSC films. The experimental constants of pinnin g are about an order of magnitude higher than those following from the critical current of the film. This resulted in an anomalously weak re sponse of the microwave properties of epitaxial HTSC films to the dc m agnetic 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 excee d 3%. The temperature dependence of the surface resistance of the mixe d-state HTSC film had a maximum near the temperature of the vortex gra te depinning. In small dc magnetic field (below 10(2)Oe), the surface resistance was observed to increase due to integrain defects.