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研究生:范儒鈞
研究生(外文):Ju-ChunFan
論文名稱:可調控自旋軌道耦合場之電子自旋磁聚焦系統
論文名稱(外文):Spin Focusing System with Controllable Rashba Spin-Orbit Interaction
指導教授:陳則銘陳則銘引用關係
指導教授(外文):Tse-Ming Chen
學位類別:碩士
校院名稱:國立成功大學
系所名稱:物理學系
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2014
畢業學年度:102
語文別:英文
論文頁數:37
中文關鍵詞:電子自旋拉什巴自旋軌道耦合磁聚焦
外文關鍵詞:SpinRashba Spin-Orbit InteractionMagnetic Focusing
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隨著科技的演進,使用電子自旋的技術勢必會成為未來的主流。根據量子力學
中的自旋軌道耦合的理論顯示出不同的電子自旋態各別擁有不同的線動量。在
本實驗中我們主要的研究方向為探究自旋上及自旋下的電子動量會如何隨著拉
什巴自旋軌道耦合場的變化而改變。我們設計出磁聚焦系統的量子裝置,其包
含了兩組一維通道,並加以垂直磁場的方式將從射出端的一維通道射出之電子
使其轉入收集端之一維通道內。因為不同動量的電子會以不同迴旋旋軌道半徑
做圓周運動,如此一來藉由這樣的方法分析收集端之一維通道的跨壓便可直接
地研究出電子動量與拉什巴自旋軌道耦合之間的關係。此外,為了研究自旋軌
道耦合場如何影響電子動量,我們另外設計了一片電極將其放置在電子做圓周
運動的區域上以達到改變拉什巴自旋軌道耦合場之強度。
本實驗的結果提供了極簡易的方法來量測拉什巴自旋軌道耦合之強度,另外
也揭示出可實際應用的層面以全電性之方式操控不同自旋態電子之動量進而加
速量子電腦的發展。
In the past time, spins were like ghosts, which everybody talked about and few
had seen. Although recently spin dynamics has been studied extensively, there are
still some unknowns about the mechanism of spin. Based on the model of spinorbit
interaction and previous experiment[1], it has been suggested that different
spin states of electrons separately own different momenta. Therefore, we would
like to know how the momentum of electrons with different spin states will vary
as a function of Rashba spin-orbit interaction. In our experiment, we design a
quantum device consisting of two quantum point contacts which are patterned in
focusing geometry. By applying a weak transverse magnetic field, two spin states
of electrons injected from one quantum point contact have different momenta and
travel in different cyclotron orbits. Through measuring focusing peak[2], we are
allowed to directly investigate the spin-orbit coupling and its influence on the spindependent
cyclotron motion. In order to see how Rashba spin-orbit interaction
will affect the momentum of electrons with different spin states, we also add a top
gate on the area of cyclotron motion to change the strength of Rashba spin-orbit
interaction. Our experimental results not only further suggest that we could use
this simple method to directly measure the strength of spin-orbit interaction in the
material but also provide an application for development of quantum computers
by an electrical control of spin-orbit interaction which reveals evidence on how
momentum are affected by spin-orbit interaction.
Abstract i
摘要ii
致謝iii
Contents iv
List of Figures vi
1 Introduction 1
2 Theoretical Background 3
2.1 Two Dimensional Electron Gas . . . . . . . . . . . . . . . . . . . . 3
2.2 Quantum Transport in 1D Transport . . . . . . . . . . . . . . . . . 4
2.2.1 Quantum Point Contact . . . . . . . . . . . . . . . . . . . . 4
2.2.2 Quantization of 1D Conductance . . . . . . . . . . . . . . . 6
2.3 Spin-Orbit Interaction . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4 Transverse Electron Focusing System . . . . . . . . . . . . . . . . . 11
3 Device and Methods 13
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Measurement Techniques 17
4.1 Cryostats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2 Measurement Circuits . . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Experimental Results 20
5.1 Magnetic Focusing . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2 Spin Separation and Periodic Focusing Peaks . . . . . . . . . . . . 22
5.3 Focusing Signal for Various Emitter Conductance . . . . . . . . . . 24
5.4 Focusing Signal for Various Rashba Spin-Orbit Interaction . . . . . 27
5.4.1 Results of Type-A . . . . . . . . . . . . . . . . . . . . . . . 27
5.4.2 Results of Type-B . . . . . . . . . . . . . . . . . . . . . . . 28
5.4.3 Variation of Parameter . . . . . . . . . . . . . . . . . . . 30
6 Conclusions 34
6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Bibliography 36
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