Microwave surface resistance in superconductors with grain boundaries

TL;DR

This paper theoretically investigates microwave surface resistance in superconductors with grain boundaries, revealing nonmonotonic dependence on critical current density and potential for lower resistance than ideal superconductors.

Contribution

It introduces a combined two-fluid and Josephson-junction model to analyze microwave dissipation in superconductors with grain boundaries, providing new insights into their surface impedance behavior.

Findings

Surface resistance depends nonmonotonically on grain boundary critical current density.

Superconductors with grain boundaries can have lower surface resistance than homogeneous ones.

Theoretical model combines intragrain and intergrain current transport mechanisms.

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.