This experimental research project focuses on unusual magnetic properties of Type II superconductors using a state of the art cryogenic scanning Hall probe microscope, with high spatial (one micrometer) and temporal resolutions. The first system to be studied is a large array of mesoscopic superconducting rings. The magnetic moments in such rings can couple "antiferromagnetically", via purely magnetic interactions, which have been observed in preliminary experiments. Cleaner arrays will be studied in a search for true long range order. The microscope will also be used to study the static and dynamic properties of vortices in superconductors with both random and periodic pinning. In the random case the primary interest is in spatially-resolved dynamics of vortices in a disordered potential, when strongly driven by either magnetic fields or applied currents, with the expectation of getting new information on the depinning transition. With periodic pinning, experiments will probe the consequences of variations of two competing length scales: the vortex-vortex spacing and the distance between pinning sites. %%% This experimental research project explores the magnetic properties of superconductors, with particular attention to how magnetic flux moves through a superconductur when pushed by an external magnetic field, or by a current passing through the superconductor. Since it is this flux motion which generally results in the loss of perfect conductivity, which is the hallmark of superconductors, a deeper understanding of these issues may lead to improved technological applications of superconductors, as in power generation and transmission. The flux motion will be imaged using the powerful new technique of scanning Hall probe microscopy. The further deve lopment of this instrument, which may find use in many fields (such as hard disk technologies) where the local structure of the magnetic field is of interest, is an integral part of the project. Results from this research may include unusual new effects or materials which may find new application in technology. This research project is interdisciplinary in nature and involves graduate students who will be excellently trained to enter positions in industry, government or education. ***
