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 the sample that allow us to image with micrometer resolution over a 150 µm 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.
Highlights
Superconducting quantum interference devices (SQUIDs) are among the most sensitive magnetic sensors available and have been widely used for magnetic imaging at cryogenic temperatures
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
Through a combination of vibration isolation in the cryostat and a rigid microscope housing, we achieve relative vibrations between the SQUID and the sample that allow us to image with micrometer resolution over a 150 μm range while the sample stage temperature remains at base temperature
Summary
Superconducting quantum interference devices (SQUIDs) are among the most sensitive magnetic sensors available and have been widely used for magnetic imaging at cryogenic temperatures. Only a few scanning probe microscopes have been reported that operate in cryogen-free DRs, including a scanning gate microscope and a scanning tunneling microscope.23 In both cases, custom spring stages were used to mechanically isolate the microscope from the cryostat. A weak thermal connection can prevent rapid measurements over a large scan window due to the heat piezoelectric elements generate while moving This is challenging when operating near the base temperature in a DR due to the limited cooling power. In principle, scanning probe microscopes are only affected by relative motion of the probe and the sample This suggests that a rigid microscope, in which the probe and the sample move together in response to the pulse-tube-induced vibrations, offers an alternative to using spring stages. To achieve an acceptable level of vibrations, we designed the microscope prioritizing rigidity while still maintaining a scan range of 150 × 150 × 100 μm and 6 × 6 × 6 mm coarse positioning range
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