MicroSQUID Force microscopy in a dilution refrigerator

Abstract

We present a new generation of a scanning MicroSQUID microscope operating in an inverted dilution refrigerator. The MicroSQUIDs have a size of 1.21$\mu$m\textsuperscript{2} and a magnetic flux sensitivity of 120 $\mu {\Phi }_0/\sqrt{\text{Hz}}$ and thus a field sensitivity of %$550^{-6}{\Phi }_0/\sqrt{\text{Hz}}$ 550$\mu \text{G}/\sqrt{\text{Hz}}$. The scan range at low temperatures is about 80 $\mu$m and a coarse displacement of 5 mm in x and y direction has been implemented. The MicroSQUID-to-sample distance is regulated using a tuning fork based force detection. A MicroSQUID-to-sample distance of 420 nm has been obtained. The reliable knowledge of this distance is necessary to obtain a trustworthy estimate of the absolute value of the superconducting penetration depth. An outlook will be given on the ongoing direction of development.

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• Electrically tunable multi-terminal SQUID-on-tip
• Visualization by scanning SQUID microscopy of the intermediate state in the superconducting Dirac semimetal PdTe${}_2$
• Multi-terminal multi-junction dc SQUID for nanoscale magnetometry