Low-temperature-compatible tunneling-current-assisted scanning microwave microscope utilizing a rigid coaxial resonator

TL;DR

This paper introduces a cryogenically compatible tunneling-current-assisted scanning microwave microscope with a rigid coaxial resonator probe, enabling high-resolution imaging of superconductors and conductors at low temperatures.

Contribution

The paper presents a novel, compact, and rigid coaxial resonator probe design for low-temperature scanning microwave microscopy, including an analysis model and successful imaging demonstrations.

Findings

Achieved ~200 nm spatial resolution in superconductor imaging.

Demonstrated stable operation at cryogenic temperatures inside a superconducting magnet.

Validated probe performance with microwave measurements on silicon wafers.

Abstract

We present a design for a tunneling-current-assisted scanning near-field microwave microscope. For stable operation at cryogenic temperatures, making a small and rigid microwave probe is important. Our coaxial resonator probe has a length of approxomately 30 mm and can fit inside the 2-inch bore of a superconducting magnet. The probe design includes an insulating joint, which separates DC and microwave signals without degrading the quality factor. By applying the SMM to the imaging of an electrically inhomogeneous superconductor, we obtain the spatial distribution of the microwave response with a spatial resolution of approximately 200 nm. Furthermore, we present an analysis of our SMM probe based on a simple lumped-element circuit model along with the near-field microwave measurements of silicon wafers having different conductivities.