Experimental Studies of Metal-Insulator Transitions and Superconductivity

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9510246 Chaikin Superconducting arrays in very high magnetic field, anisotropic superconductors, as well as normal metals and two dimensional heterostuctures will be studied. The ultimate goal of these studies is to test for the existence of extended, localized and commensurate states in different controllable potentials, to image these states, and to study their dynamics. Superconducting wire networks designed to interact with a penetrating flux lattice will be fabricated using lithographic techniques. This work will focus on the effect of anisotropy where striking theoretical predictions have been made, about localization, anisotropic commensurability, and temperature dependent flux lattice configurations. The pinning and dynamics of Josephson vortices in bulk superconductors will be further investigated. The exciting theoretical prediction of magnetic field induced one dimensionalization of the electrons and the resulting re- establishment of superconductivity at high magnetic field will also be experimentally tested using high purity organic superconductors. In another experiment, novel lithographic techniques based on self assembly of block copolymers, will be used to fabricate "nano" periodic potentials (~ 300Ao spacing) on normal metals, superconductors and quantum Hall devices. This will allow the study of a new regime where the periodic potential is comparable to magnetic lengths and much shorter than many characteristic dephasing and scattering length. %%% Superconducting arrays in very high magnetic field, anisotropic superconductors, as well as normal metals and two dimensional heterostuctures will be studied. Specifically this research will address the question of how the well understood periodic potentials can be extended to quasi-periodic potentials where there are competing length scales and different types of anisot ropy. Superconducting wire networks designed to interact with a penetrating flux lattice will be fabricated using lithographic techniques. This work will focus on the effect of anisotropy where striking theoretical predictions have been made, about localization, anisotropic commensurability, and temperature dependent flux lattice configurations. The pinning and dynamics of Josephson vortices in bulk superconductors will be further investigated. The exciting theoretical prediction of magnetic field induced one dimensionalization of the electrons and the resulting re- establishment of superconductivity at high magnetic field will also be experimentally tested using high purity organic superconductors. In another experiment, novel lithographic techniques based on self assembly of block copolymers, will be used to fabricate "nano" periodic potentials on normal metals, superconductors and quantum Hall devices. This will allow the study of a new regime where the periodic potential is comparable to magnetic lengths and much shorter than many characteristic lengths. ***