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Vortex Matter and Magnetic Flux Periodicity in Mesoscopic Superconductors
Author: WangShanShan
Tutor: ChaGuoQiao
School: Shanghai University
Course: Condensed Matter Physics
Keywords: Mesoscopic superconductor Flux periodicity Vortex state Antivortex
CLC: O488
Type: Master's thesis
Year: 2013
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Abstract
Modern nanofabrication techniques enable one to make very small superconducting samples with various geometries. With the size of the sample is decreased, itcould be seen some characteristics different from the macroscopic systems due to thequantum size effect. For mesoscopic superconductors with size comparable to thecoherence length or the penetration depth, the properties of the systems areconsiderably influenced by the size and geometry of the sample, and then many novel phenomena are induced. In the present thesis, the flux periodicity in mesoscopicsuperconducting loops and the vortex configuration and dynamics in square mesoscopic superconducting cylinders with a centered hole are investigated based on theBogoliubovde Gennes (BdG) theory and the timedependent GinzburgLandau(TDGL) theory. Main results are summarized as follows:(1) The quantum phase transition in mesoscopic noncircular loops threaded byan AharonovBohm flux is systematically investigated by numerically solving theBdG equations selfconsistently. We focus on the magnetic flux dependence of theswave superconducting order parameter and current in symmetric and asymmetricsamples. The influence of surface indentation or bulge defects positioned at the inneror outer edge of the sample on the periodic oscillation is also discussed. We findvarious hc/eflux periodicity evolution patterns, and the periodic phase transitionsbetween the superconducing state and the resistive/normal state are demonstratedbesides the superconducing state transitions. Our investigation may shed new lighton material engineering and provide important insights to designing superconductingquantum devices.(2) The vortex configuration in square mesoscopic superconducting cylinderswith a centered hole is investigated by numerically solving the semidiscretizedTDGL equations. Comparing with the perfect square cylinders, we can clearly find the differences in vortex configuration for the square cylinders with a hole. Furthermore, we demonstrate the effect of inner boundary on the ways of vortex entry andexit from the sample as well as the vortex structures.(3) The vortex dynamics under applied current in square mesoscopic superconducting cylinder with a hole is investigated by numerically solving thesemidiscretized TDGL equations. We find that the creation and annihilation of thevortex and antivortex as well as the directed vortex motion can be generated by manipulating the applied magnetic field or current. We also investigate the magnetization of the system when the GinzburgLandau parameter and the magnetic field andcurrent are varied. The phenomena of paramagnetism, diamagnetism, and the periodic transition between them are displayed.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Mesoscopic Physics
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