Effects of Intrinsic and Disorder-Induced Anisotropies on the Vortex Dynamics and Superconducting Gap of High-Temperature Superconductors-From Macroscopic to Microscopic Scales

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w:\awards\awards96\num.doc 9705171 Yeh This experimental research project focuses on the vortex dynamics and vortex-pinning of anisotropic cuprate superconductors, emphasizing a wide range of length- and excitation-frequency scales. Two goals of the work are to investigate competition between the intrinsic and disorder-induced anisotropies on the vortex pinning and dynamics of cuprate crystals and films with different static disorder; and to study the thermally-induced and current-driven vortex dynamics from macroscopic to microscopic scales. Experiments include measurement of the Hall conductivity up to 10MHz; the first- and third-harmonic ac magnetic susceptibility from 0.1Hz to 0.1MHz, and the microwave magneto- impedance from 6 to 26 GHz using high-Q sapphire-loaded microwave cativites. Scanning tunneling microscope measurements will also be made. %%% This experimental research project is centered on the effects of magnetic field on the cuprate high temperature superconductors, which are important in potential applications such as filters for communication systems and current carrying wires for power transmission. The research focuses on the stability of the magnetic flux lines as they penetrate the superconductor, the types of motions of the flux lines and how to minimize such motions by providing so-called pinning centers. Flux line motions lead to internal energy loss and heating and are detrimental to efficiency in most applications. The experimental tools in this project include measurement of harmonic generation in the interaction of ac magnetic fields with such samples, and study of vortex geometries using the scanning tunneling microscope. 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. ***