Scanning SQUID microscopy in a cryogen-free dilution refrigerator

TL;DR

This paper presents a cryogen-free dilution refrigerator setup with a scanning SQUID microscope capable of imaging magnetic fields at millikelvin temperatures with micrometer resolution, suitable for studying superconducting devices.

Contribution

Development of a cryogen-free dilution refrigerator compatible scanning SQUID microscope with vibration isolation and high-resolution magnetic imaging capabilities.

Findings

Achieved stable imaging at 30 mK with micrometer resolution.

Simultaneous imaging of static magnetic fields, susceptibility, and device-generated fields.

Demonstrated imaging of a superconducting micrometer-scale device.

Abstract

We report a scanning superconducting quantum interference device (SQUID) microscope in a cryogen-free dilution refrigerator with a base temperature at the sample stage of at least 30 mK. The microscope is rigidly mounted to the mixing chamber plate to optimize thermal anchoring of the sample. The microscope housing fits into the bore of a superconducting vector magnet, and our design accommodates a large number of wires connecting the sample and sensor. Through a combination of vibration isolation in the cryostat and a rigid microscope housing, we achieve relative vibrations between the SQUID and sample that allow us to image with micrometer resolution over a 150 $\mu$m range while the sample stage temperature remains at base temperature. To demonstrate the capabilities of our system, we show images acquired simultaneously of the static magnetic field, magnetic susceptibility, and magnetic fields produced by a current above a superconducting micrometer-scale device.