Microwave performance of high-density bulk MgB2

TL;DR

This study investigates the microwave surface resistance of high-density MgB2 superconductors, showing that surface polishing reduces resistance and that the material's high density and grain connectivity lead to low microwave losses.

Contribution

The paper demonstrates that high-density HIPed MgB2 exhibits low microwave surface resistance and that surface polishing significantly improves microwave performance.

Findings

Surface resistance decreases by 40% after polishing.

Surface resistance is independent of microwave magnetic field up to 4 Oe.

Overall low surface resistance (~0.8 mOhms at 10 GHz and 20 K).

Abstract

We have performed microwave measurements on superconducting hot-isostatically- pressed (HIPed) bulk MgB2 using a parallel-plate resonator technique. The high density and strength of the HIPed material allowed preparation of samples with mirror-like surfaces for microwave measurements. The microwave surface resistance decreased by about 40% at 20 K when the root-mean-square surface roughness was reduced from 220 nm to 110 nm through surface-polishing and ion-milling. The surface resistance was independent of surface microwave magnetic field at least up to 4 Oe and below 30 K. We attribute this behavior, and the overall low surface resistance (~0.8 mOhms at 10 GHz and 20 K), to the high density of our samples and the absence of weak links between grains.