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Transport Properties of Spin Electron in Quantum Point Contact

Author: ZhangJian
Tutor: LiuJianJun
School: Hebei Normal
Course: Condensed Matter Physics
Keywords: conductance quantization quantum point contact density functional theory Green’s function technique scanning probe microscope techniques
CLC: O471.1
Type: Master's thesis
Year: 2010
Downloads: 131
Quote: 0
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Abstract


The quantum characteristic of mesoscopic system has been observed in experiments, though the mesoscopic system is macroscopical. Because of its abundant physics characteristic, the mesoscopic system has been investigated experimentally and theoretically. Quantum point contact, quantum wire and quantum dot are common experimental models. Electrons keep phasic memory in the transport process in mesoscopic system, thus abnormal quantum interference and quantum phenomenon depended on mesoscopic size are induced. Conductance quantization effect is the most remarkable quantum phenomenon. The conductance anomaly called 0.7 structure has been observed in QPCs. In order to find out the origin of this phenomenon, the mesoscopic device interior structure and the electron flow and electric charge distribution are researched experimentally by scanning probe microscope. The different results can be achieved via the use of SPM. Based on recursive Green’s-function technique, we have studied the conductance of QPC affected by Rashba spin-orbit coupling, magnetic field and the tip of SPM.In conclusion, the QPC system is divided into M×N lattices, the sites of the lattice are denoted as ( n, m), where n = 1, 2,K,N and m = 1, 2,K,M. The effects of tip on conductance are enhanced by the tip scanning over the sample closed to the QPC centre along parallel and perpendicular electron transport direction. These calculated results are consistent with Topinka’s experimental conclusions. We now discuss the effect of a perpendicular magnetic field on conductance. As the perpendicular magnetic field increasing the conductance of QPC vs V_g and the transfer mode number is increased periodically. For a given gate voltage and a higer perpendicular magnetic field, the conductance and the oscillations amplitude induced by spin-obit coupling are increased. Meanwhile, the effects of tip on conductance are also diminished. These results can be excellently explained by Shubnikov-de Haas effects. Our theoretical results disclose that the charge distribution and electron transport in the material can be obviously affected by the magnetic field and the tip, which will provide us a new concept for microelectronic devices design.

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CLC: > Mathematical sciences and chemical > Physics > Semiconductor physics > Semiconductive Theory > Semiconductor quantum theory
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