Constructing and Characterizing a Scanning SQUID Microscope for a Cryogen Free Dilution Refrigerator

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Abstract

Superconducting quantum interference devices, or SQUIDs, are highly sensitiveto magnetic flux and can be used to perform magnetic imaging at cryogenic tem- peratures. In this dissertation, I describe the first scanning SQUID microscope in a cryogen-free dilution refrigerator. First, I briefly describe basic SQUID theory, how to perform scanning SQUID microscopy, and how to design SQUIDs suited for microscopy. Next, I discuss both the apparatus and method to systematically characterize SQUIDs. I demonstrate that while heuristics provide guidance for finding low noise operating points, one often misses the best noise performance of the SQUID found by a systematic search. I also briefly discuss how to use ma- chine learning to predict SQUID noise. I then describe in depth the design of the SQUID microscope, focusing on explaining the reasons behind various features of the coldfinger and microscope. Finally, I describe how to characterize vibrations in our microscope using images of a vortex in a superconductor.

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122 pages
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2021-12
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Fuchs, Gregory David
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Selman, Bart
Nowack, Katja C.
Degree Discipline
Applied Physics
Degree Name
Ph. D., Applied Physics
Degree Level
Doctor of Philosophy
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Government Document
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Attribution 4.0 International
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dissertation or thesis
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