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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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Modern nanofabrication techniques enable one to make very small supercon-ducting 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 nov-el phenomena are induced. In the present thesis, the flux periodicity in mesoscopicsuperconducting loops and the vortex configuration and dynamics in square mesos-copic superconducting cylinders with a centered hole are investigated based on theBogoliubov-de Gennes (BdG) theory and the time-dependent Ginzburg-Landau(TDGL) theory. Main results are summarized as follows:(1) The quantum phase transition in mesoscopic noncircular loops threaded byan Aharonov-Bohm flux is systematically investigated by numerically solving theBdG equations self-consistently. We focus on the magnetic flux dependence of thes-wave 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/e-flux 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 semi-discretizedTDGL equations. Comparing with the perfect square cylinders, we can clearly find the differences in vortex configuration for the square cylinders with a hole. Further-more, 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 super-conducting cylinder with a hole is investigated by numerically solving thesemi-discretized TDGL equations. We find that the creation and annihilation of thevortex and antivortex as well as the directed vortex motion can be generated by ma-nipulating the applied magnetic field or current. We also investigate the magnetiza-tion of the system when the Ginzburg-Landau parameter and the magnetic field andcurrent are varied. The phenomena of paramagnetism, diamagnetism, and the peri-odic transition between them are displayed.

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