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 $\mu\Phi_{0} / \sqrt{\textrm{Hz}}$ and thus a field sensitivity of %$550^{-6} \ \Phi_{0} / \sqrt{\textrm{Hz}}$ 550$ \ \mu \textrm{G}/ \sqrt{\textrm{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.