Persistent Currents in Normal Metal Rings (Yale PhD thesis)

TL;DR

This thesis reports high-sensitivity measurements of persistent currents in normal metal rings using cantilever torsional magnetometry, revealing currents as low as 1 pA and exploring their dependence on magnetic field, temperature, and sample orientation.

Contribution

It introduces a highly sensitive measurement technique for persistent currents and extends the understanding of their behavior under various experimental conditions.

Findings

Measured persistent currents as low as 1 pA

Extended the temperature and magnetic field range for observing persistent currents

Characterized the dependence of current on sample orientation and number of rings

Abstract

In this work, I present measurements of persistent currents in normal metal rings performed with cantilever torsional magnetometry. With this technique, the typical persistent current (the component that varies randomly from ring to ring) was measured with high sensitivity. I report measured magnitudes as low as 1 pA, over two orders of magnitude smaller than that observed in previous studies. These measurements extend the range of temperature and magnetic field over which the typical current has been observed. The wide magnetic field range allowed us to study the effect of magnetic field penetrating the ring. It also enabled the recording of many independent measurements of the current magnitude in a single sample. These independent measurements are necessary to characterize the persistent current magnitude because it is a random quantity. From these measurements of the persistent current, I also characterize the parametric dependence of the typical current on sample orientation and number of rings. In addition to presenting the experimental results, I thoroughly review the theory of the typical persistent current in the diffusive regime. I begin with the simplest model and build up to the case appropriate for the samples studied in our experiments. I also present in detail the experimental apparatus used to measure the persistent currents.