Nano-SQUID susceptometry and fluctuation effects in superconducting rings

TL;DRAbstract

This thesis is broken down into two main components: the design and implementation of two generations of Scanning Superconducting Quantum Interference Device (SQUID) sensors, and the use of these tools to describe several kinds of fluctuations that can significantly affect the properties of micron sized aluminum rings. The first chapter describes the susceptometer that was used for the bulk of the ring experiments. In it, I outline the advantages of a multi-layer design with local field coils and integrated feedback loops. To reach the fundamental sensitivity limits set by Johnson noise in the device itself, I employed piezo electric positioners to measure background magnetic fields, in addition to taking images of the magnetic field. The second chapter describes a generation of SQUIDs with FIB-patterned pickup loops that are connected to a similar base design. The coupling to ultra-small objects is significantly enhanced by the pickup loop's small diameter (down to ∼ 600 nm) and reduc

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