Mesoscopic Magnetic Measurements

Stanford University, Stanford CA

Investigators

Abstract

Technical A normal metal ring that is smaller than the decoherence length is expected to have a persistent current that is periodic in the flux through the ring. Such a persistent current is a signature of phase coherence in an electronic system, and provides a means to test models and theories of the electronic state. This project will use a scanning Superconducting QUantum Interference Device (SQUID) microscope in a dilution refrigerator to study ballistic metal rings (in which the electron mean free path is comparable to the circumference) and to directly measure the distribution of currents in an ensemble of nominally identical rings. This distribution will provide information on the role of disorder and interactions in quantum metals. The scanning approach allows the measurement of the properties of many mesoscopic samples in each cooldown, one sample at a time. These highly demanding experiments will provide the educational benefit of training some of the nation?s top young scientists in an intellectually rich research environment. Research students will learn nanotechnology and precision measurement techniques as well as fundamental physics. In addition, lab personnel interact actively with the K-12 science education community through a Summer Institute for Middle School Teachers. Non-technical It is well known that currents in superconducting rings can flow indefinitely because superconductors have zero resistance. Such currents are called ?persistent? currents. Less well known is that normal metals -- even though they are resistive -- are also theoretically expected to have persistent currents when they are sufficiently small and cold. These persistent currents are a direct signature of the quantum mechanical, wavelike nature of the electrons in the metal, and provides a means to test models and theories of the electronic state. This project will use an ultrasensitive magnetic detector, called a Superconducting QUantum Interference Device (SQUID), at very low temperatures to study persistent currents in order to test our understanding of the quantum-mechanical nature of metals and semiconductors. These highly demanding experiments will provide the educational benefit of training some of the nation?s top young scientists in an intellectually rich research environment. Research students will learn nanotechnology and precision measurement techniques as well as fundamental physics. In addition, lab personnel interact actively with the K-12 science education community through a Summer Institute for Middle School Teachers.