Experimental Study of the Magnetic Flux Line Lattice in Superconductors

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w:\awards\awards96\num.doc 9705389 Andrei This experimental research project focuses the interactions between quantized magnetic flux lines threading through a Type II superconductor. An ordered state of interacting flux lines, as theoretically predicted by Abrikosov, provides the conceptual basis of the experimental work. The influences of material disorder, thermal fluctuations, and the quantum nature of the flux line formation lead to an extremely complicated picture in the area of parameters where the Abrikosov lattice becomes unstable. There are questions relating to a glassy phase of the flux array, among others, which are addressed in this experimental project. The work on 2H-NbSe2 identified two states of the flux line lattice characterized by dramatically different dynamics, one being disordered and have pinning frequencies two orders of magnitude higher than the ordered lattice, and accompanied by much higher critical currents. In this project local magnetization measurements will be made using an array of microscopic Hall sensors realized in the 2-D electron gas at the interface of a GaAs/GaAlAs heterostructure. Other work includes DC and AC measurements of the shear modulus of the flux array, and measurements of transverse currents in dynamic fluxon states. Portions of the work will be done in collaboration with Dr. Eli Zeldov of the Weizmann Institute. %%% This experimental research project, is focused on the behavior of Type II superconductors in a magnetic field. In this case the magnetic field can penetrate the superconductor, in an array of quantized flux lines. Under ideal conditions these lines, each carrying one quantum of magnetic flux, arrange in an ordered array or flux lattice, as predicted theoretically by Abrikosov. This experimental project is devoted to measurement of the motions and arrangements o f the flux lines in less than ideal conditions when the flux lines may be in a disordered state or in a state of motion somewhat like a liquid. The results of this research may provide information of importance to the application of Type II superconductors including high temperature cuprate superconductors in improved electrical and electromechanical 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. ***