On the mechanism of non-resonant microwave absorption in granular high-temperature superconductors

Abstract

The authors investigate the mechanisms of microwave (MW) losses in granular YBa2Cu3Ox at weak magnetic fields in a wide temperature range. The MW losses are believed to arise on the shunt resistances of junctions creating the weak-link network. Magnetic field enhances the ohmic losses in the junctions by increasing the resistive portion of MW currents due to increased junction inductance. The hysteretic features of the MW losses are described in terms of the intergranular critical state model with the additional influence of intragranular magnetization and the interaction of inter- and intragranular vortices. A model of modulated MW absorption is introduced, based on the idea of modulation of the intergranular critical state magnetization current. Theoretical calculations are shown to fit the experimental low-field MW absorption results.