High-frequency dissipation in high- Tc superconductors at low magnetic field

Abstract

The complex mechanism of high-frequency dissipation in high-temperature superconductors is discussed. The dissipation is due to the presence of thermally excited carriers, vortex motion, and the existence of inter- and intragrain Josephson junctions in superconducting material. At a low magnetic field, the superconducting sample can be modeled as a network of resistively shunted Josephson junctions. A comparison between the single- and double-contact model is presented. Considering the properties of the network of resistively shunted, symmetric double contracts irradiated by the microwaves, one obtains a consistent description of the high-frequency dissipation in ceramics and single crystals at a low magnetic field. The different distribution of effective areas of junctions and superconducting loops explains a variety of the magnetic field dependences of high-frequency dissipation observed in ceramics of different porosity, texture, and grain size, as well as in single crystals. The proposed model allows one to distinguish the extrinsic and intrinsic high-frequency properties of high-temperature superconductors.