Superconducting Pinning with Artificially Prepared Nanostructures

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Non Technical AbstractVortices are prevalent in nature all the way from the atmosphere, charge and uncharged plasmas, magnetic and superconducting materials. An important issue in this field is the way to anchor these vortices, the so called "pinning" because physical properties are modified in fundamental ways if vortices are pinned. A particularly interesting physical situations arises in superconductors where the magnetic field penetrates the material by the formation of arrays of superconducting vortices. These vortices can be pinned by artificially prepared pinning arrays which can be produced using novel lithographic techniques. This project is dedicated to the study of fundamental issue which arise when superconducting vortices interact with nanostructured arrays. Issues such as the effect of the array geometry, materials, shape of the pinning sites will be studied.In addition to its basic research interest, these studies may lead to schemes for reducing spontaneous noise and enhancing the superconducting properties of the material.Technical AbstractThe study of vortex pinning in superconductors is an interesting basic research area, with implications for the fabrication of high critical current tapes and low noise superconducting devices. The interaction between artificially prepared pinning arrays and the superconducting vortex lattice leads to quantum matching phenomena which manifest as enhanced critical currents and decreased resistance at particular fields. This research project, will be dedicated to (a) finding the type of pinning structure which individually provides strong pinning of vortices, and (b) introducing appropriate "defects" within the periodic array of pins, such as stripes and/or random fluctuations on the pinning site positions. (a) will increase the domain wall energy for the periodic point pins and increase the magnetic field width for the periodic stripe pins, thereby reducing thermal fluctuations, while (b) can change the universality class of the commensurate phase, thereby suppressing thermal fluctuations in fundamental ways. The issues concerning (a) are mostly material-specific, involving the microscopic mechanism of individual vortex-pin interaction. The issues concerning (b) are statistical in nature, having to do with the collective interaction of the vortex lattice with the array of pins. Both of these issues will be investigate systematically, and through extensive experimental collaborations and interactions with theoretical groups active in the field.