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研究生:鄭鈞之
研究生(外文):Chun-ChihCheng
論文名稱:量子線之電子溫度研究
論文名稱(外文):ELECTRON TEMPERATURE OF BALLISTIC CURRENT IN QUANTUM POINT CONTACT
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:物理學系碩博士班
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:2012
畢業學年度:100
語文別:英文
論文頁數:61
中文關鍵詞:量子線電子溫度
外文關鍵詞:Quantum Point ContactElectron Temperature
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最近幾年來,量子線在許多實驗上分別被證實可以利用電流不僅產生以及操作自旋極化,還可以產生自旋電流 [1, 2, 3]。實驗上證實,透過自旋-軌道交互作用或是極大的偏壓可以將系統的動量簡併態分開,藉此產生自旋電流。由此可知,量子線在未來不管是自旋電子學或是量子資訊的研究都有重要的應用。然而,現階段科學家們對量子線其他物理性質的瞭解還不夠完善,使得量子線至今依然無法徹底地發揮它的效用。
本實驗將會呈現利用量子點當溫度計,來研究電子通過量子線做傳輸後的溫度變化。進一步的,本實驗將會對量子線加偏壓,研究此情況下量子線溫度的特性。本實驗的研究想法如下:實驗的樣品具備了一個量子線以及量子點,電子會由量子線通過,再透過加磁場的方式讓電子通過量子點。如此一來,就可以得到量子點的庫倫阻擋震盪曲線,而曲線中的峰值就可以用來量測電子通過量子線後的溫度變化。
實驗結果顯示,電子通過量子線後並不會有溫度的變化,這告訴我們電子通過量子線的傳輸是沒有非彈性碰撞產生的。更重要的是,這代表著電子的自旋並不會受到偏壓的影響。這樣的結果對未來不管是自旋電子學或是量子資訊的研究,都有種要的影響。
Quantum point contacts (QPC), i.e., quasi one-dimensional (1D) conductors, have recently been suggested to form the basis of a fully electrical method for the creation and manipulation of spin polarization as well as spin-polarized current [1,2,3]. It has been shown that the all-electric spin injection can be achieved when the momentum degeneracy is lifted either by spin-orbit interaction or a large source-drain dc bias. However, there has been little understanding of other physical properties about the QPC, which remains of significant importance before its application in future spintronics and quantum information processing can be achieved.

I will demonstrate the temperature measurement of the electron transport through a QPC using the intrinsic property of quantum dot (QD). Moreover, I will show the temperature properties of QPC in the non-Ohmic regime wherein a dc source-drain bias was applied. The idea is the following: a device is constituted of a QPC, serving as a charge/spin injector, and a QD, which acts as a detector in this work. The electrons will be injected through the QPC from a source, and tunnel into the QD due to an applied magnetic field causing it to rotate, Coulomb blockade oscillations were then observed and the resonance peaks were used as a thermometer to measure the temperature dependence of the electrons of current in the QPC.

The result shows that the temperature will not change during the transportation, which implies that it may be a ballistic transport for electron through a QPC which shows that the spin relaxation would be little affected by source-drain bias, which is important for spintronics and quantum information processing.
摘要 I
ABSTRACT II
ACKNOWLEDGEMENT III
CONTENTS IV
LIST OF FIGURES VI
1. INTRODUCTION 1
2. THEORETICAL BACKGROUND 4
2.1 ONE-DIMENSIONAL QUANTUM TRANSPORT 4
2.1.1 Landauer-Büttiker formula 6
2.1.2 Quantization of 1D conductance 12
2.1.3 Non-linear transport 13
2.2 ZERO-DIMENSIONAL QUANTUM TRANSPORT 15
3. EXPERIMENT SETUP 20
3.1 CRYOSTATS 20
3.2 MEASUREMENT TECHNIQUE 22
4. MEASUREMENT 24
4.1 DEVICE 24
4.2 METHOD 25
4.3 EXPERIMENTAL RESULTS 26
4.3.1 CB dc spectroscopy and T-dependence of CB versus Vsd-1d 28
4.3.2 CB for various Vsd-1d and Temperature with a smaller dot 36
4.3.3 CB temperature-dependence at Vsd-1d = 0 38
5. CONCLUSION 43
REFERENCE 45
APPENDIX A 47
APPENDIX B 57
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[3] T.-M. Chen, A. C. Graham, M. Pepper, I. Farrer, D. Anderson, G. A. C. Jones, and D. A. Ritchie, Direct Observation of Nonequilibrium Spin Population in Quasi-One-Dimensional Nanostructures, Nano Letter 10, 2330 (2010).
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[7] T. J. Thornton, M. Pepper, H. Ahmed, D. Andrews, and G. J. Davies, One-Dimensional Conduction in the 2D Electron Gas of a GaAs-AlGaAs Heterojunction, Phys. Rev. Lett. 56, 1198 (1986)
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[11] T.-M. Chen, Ph.D. thesis, University of Cambridge, UK (2009)
[12] L. I. Glazman and A. V. Khaettskii, Nonlinear Quantum Conductance of a Lateral Microconstraint in a Heterostructure, Europhys. Lett. 9, 263 (1989).
[13] L. Martin-Moreno, J. T. Nicholls, N. K. Patel, and M. Pepper, Non-linear conductance of a saddle-point constriction, J.P.C.M., 4, 1323 (1992)
[14] A. Fuhrer, Ph.D. thesis, Swiss Federal Institute of Technology, Switzerland (2003).
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