Microwave surface resistance of superconductors with grain boundaries

Abstract

Microwave-field distribution, dissipation, and surface impedance are theoretically investigated for superconductors with laminar grain boundaries (GBs). In the present theory we adopt the two-fluid model for intragrain transport current in the grains, and the Josephson-junction model for intergrain tunneling current across GBs. Results show that the surface resistance ${R}_{s}$ nonmonotonically depends on the critical current density ${J}_{cj}$ at GB junctions, and ${R}_{s}$ for superconductors with GBs can be smaller than the surface resistance ${R}_{s0}$ for ideal homogeneous superconductors without GBs.