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CPM Seminar
superconducting, magnetic and hybrid V. Metlushko
Department of Electrical Engineering and Computer Science Within the last few years it has been realized that the remarkable properties of superconducting thin films containing a periodic array of defects (such as sub-micron sized holes) offer a new route for developing a new superconducting materials based on precise control of microstructure by modern lithography. The value of the critical current is determined by the balance of Lorentz forces and pinning forces acting on the flux lines in the superconductor. Lorentz forces proportional to the current flow tend to drive the flux lines into motion, which dissipates energy and destroys zero resistance. Pinning forces created by isolated defects in the microstructure oppose flux line motion and increase the critical current. Many kinds of artificial pinning centers have been proposed and developed to increase critical current performance, ranging from dispersal of small non-superconducting second phases to creation of defects by proton, neutron or heavy ion irradiation. In all of these methods, the pinning centers are randomly distributed over the superconducting material, causing them to operate well below their maximum efficiency. We are overcoming this drawback by creating pinning centers on a periodic lattice so that each pin site interacts strongly with only one or a few flux lines. Tailoring the size of the pin sites and the period and symmetry of the pinning lattice enables a precise control of the critical current.
Thursday, November 16th 2000, 15:30 |