電子在低維度之下所展現的物理現象被視為打開下一個科技世代的鑰匙。在過去幾十年大部分的現象已逐漸被發現和解釋成功,然而當電子束縛在一維的量子線中我們可以觀察到一個很特殊的物理現象,即0.7 效應。 由於它的形成原因至今仍無法完整解釋, 吸引了許多科學家的注意,想揭露其神秘的面紗。 2002, 哈佛大學的S. M. Cronenwett 提出了一個很特別的解釋說法 — 類近藤效應模組。他們的數據顯示 0.7 效應會隨著溫度的變化而改變,這跟近藤效應非常相似。同時也在量子線中觀察到近藤效應的另一個物理特徵,即"非尋常零偏壓效應"。然而,一般我們所認知的近藤效應是由於傳導電子和束縛電子交互作用而產生的, 所以這現象只能在可以將電子束縛在零維空間的量子點觀察到。 物理現象衍生出的矛盾使得我們必須去思考一個問題,"一維的量子線是否也有能力將電子束縛住?"
N. J. Cragi 和他的同事在2005年的一篇論文給了我們靈感,在本實驗中我們將量子點和量子線結合在一起形成一耦合系統去研究量子線是否可以束縛電子。而在這篇論文中我將會展示兩種不同結構所測量到的數據。 實驗一開始我們先證明我們的量子線中同樣可以觀察到"非尋常零偏壓效應", 接著將量子線和量子點耦合,並且改變量子點內所束縛的電子數目看量子線中的非尋常零偏壓效應是否會因此而改變。 實驗顯示,當量子點內的電子數目調整為偶數時,可以觀察到非尋常零偏壓效應,相反地,如果電子數目是奇數時,由於RKKY交互作用,我們發現非尋常零偏壓效應消失了。 本實驗數據顯示近藤效應及束縛電子的確存在於一維量子線中,此結果對相關議題提供了極具參考價值的實驗證據。

One of the inviting phenomena in mesoscopic physics is the 0.7 structure forming in the one-dimensional confinement field called quantum wires. Owing to the unknown origin, it stimulates numerous interesting studies in this special effect. The most attractive argument is the “ Kondo – like” model brought up by S. M. Cronenwett et al. They presented evidence that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state. However the Kondo effect in principle should occur only in closed systems, like quantum dots as a result of tunneling of singlet formed by the coupling between localized spin and conduction electrons. Now, a big question emerges. “ Do localized spins exist in quantum wires ? ”
Inspired by the idea of N. J. Cragi et al. , here we utilize devices formed by a quantum dot coupled with a quantum wire to investigate whether there is any localized spin existing in quantum wires. This thesis presents two geometries of devices. At first, by pinching off the quantum dot next to the quantum wire, we show that the quantum wires can exhibit the Kondo-like characteristics , i.e. zero bias anomaly. Instead of pinching the dot off, in the next step we keep it open and couple with quantum wire to form one system. Through changing the number of electrons in quantum dot, the RKKY interaction dominate this coupling region; therefore, one can observe the change of zero-bias peak. When the dot contains odd number of electrons, the zero-bias peak will disappear ; in contrast, if the dot contains even number of electrons then we can observe zero-bias peak. This result shows that the Kondo-effect and localized spin indeed exists in the one-dimensional system.

[1] Moore, Gordon E. (1965). "Cramming more components onto integratedcircuits". Electronics Magazine. p.4. Retrieved 2006-11-11.
[2] "1965 – "Moore's Law" Predicts the Future of Integrated Circuits". Computer History Museum. 2007. Retrieved 2009-03-19.
[3] Michael Kanellos (2003-12-01). "Intel scientists find wall for Moore's Law". CNET. Retrieved 2009-03-19.
[4] Landauer, R. Irreversibility and heat generation in the computing process. IBM J. Res. Dev.5,183–191 (1961).
[5] A. Kristensen et al., Phys. Rev. B 62, 10950 (2000).
[6] S. M. Cronenwett et al., Phys. Rev. Lett. 88, 226805 (2002).
[7] H. L. St¨ormer, R. Dingle, A. C. Gossard,W. Wiegmann, and M. D. Struge, Sol. St. Commun. 29, 705 (1979).
[8] Effendi Leobandung, Lingjie Guo, Yun Wang, and Stephen Y. Chou, J. Vac. Sci. Technol. B, Vol. 13, No. 6, Nov/Dec 1995.
[9] For a review, see L. P. Kouwenhoven et al., Mesoscopic Electron Transport, Proceedings of the NATO Advanced Study Institute, L. Sohn, L. P. Kouwenhoven, G. Schön, Eds., Curaçao, 25 June to 5 July 1996 (Series E, 345, 105, Kluwer, Dordrecht, Netherlands, 1997).
[10] Beenakker, C.W.J., Theory of Coulomb-Blockade Oscillations in the Conductance of a Quantum Dot. Physical Review B, 1991. 44(4): p. 1646.
[11] W. Meissner and B. Voigt, Ann. Phys. 7, 761 (1930).
[12] W. Meissner and B. Voigt, Ann. Phys. 7, 892 (1930).
[13] J. Kondo, Prog. Theor. Phys. 32, 37 (1964).
[14] Leo Kouwenhoven and Leonid Glazman,Physics World, January, 2001
[15] Y. Meir, N. S. Wingreen, and P. A. Lee, Phys. Rev. Lett. 70, 2601 (1993).
[16] L. I. Glazman and M. E. Raikh, JETP Lett. 47, 452 (1988).
[17] T. K. Ng and P. A. Lee, Phys. Rev. Lett. 61, 1768 (1988).
[18] N. S. Wingreen and Y. Meir, Phys. Rev. B 49, 11040 (1994).
[29] P. W. Anderson, Phys. Rev. 124, 41 (1961).
[20] D. Goldhaber-Gordon et al., Phys. Rev. Lett. 81, 5225 (1998).
[21] N. E. Bickers, Rev. Mod. Phys. 59, 845 (1987).
[22] J. Kondo in Solid State Physics, H. Ehrenreicht, F. Seitz, D. Turnbull, Eds.(Academic, New York, 1969), vol. 23, p. 183.
[23] Y. Meir, N. S. Wingreen, and P. A. Lee, Phys. Rev. Lett. 70, 2601 (1993).
[24] S. M. Cronenwett, T. H. Oosterkamp, and L. P. Kouwenhoven, Science 281, 540 (1998).
[25] D. A. Wharam, T. J. Thornton, R. Newbury, M. Pepper, H. Ahmed, J. E. F. Frost, D. G. Hasko, D. C. Peacock, D. A. Ritchie, and G. A. C. Jones, J. Phys. C 21, 209 (1988).
[26] B. J. van Wees, H. van Houten, C. W. J. Beenaker, J. G. Williamson, L. P. Kouwenhoven, D. van der Marel, and C. T. Foxon, Phys. Rev. Lett. 60, 848 (1988).
[27] B. J. van Wees, L. P. Kouwenhoven, H. van Houten, C. W. J. Beenakker, J. E. Mooij, C. T. Foxon, and J. J. Harris, “Quantized conductance of magnetoelectric subbands in ballistic point contacts,” Phys. Rev. B, vol. 38, p.3625, 1988.
[28] K. J. Thomas, J. T. Nicholls, M. Y. Simmons, M. Pepper, D. R. Mace, and D. A. Ritchie, “Possible spin polarization in a one-dimensional electron gas,” Phys. Rev. Lett., vol. 77,135, 1996.
[29] B. J. vanWees, L. P. Kouwenhoven, E.M.M.Willems, C. J. P.M. Harmans, J. E. Mooij, H. van Houten, C. W. J. Beenakker, J. G. Williamson, and C. T. Foxon, “Quantum ballistic and adiabatic electron transport studied with quantum point contacts,” Phys. Rev. B, vol. 43, p.12431, 1991.
[30] J. Nygard, D. H. Cobden, and P. E. Lindelof, Nature 408, 342 (2000).
[31] D. Goldhaber-Gordon et al., Nature 391, 156 (1998).
[32] D. Goldhaber-Gordon et al., Phys. Rev. Lett. 81, 5225 (1998).
[33] W. G. van der Wiel et al., Science 289, 2105 (2000).
[34] Y. Meir, K. Hirose, and N. S. Wingreen, Phys. Rev. Lett. 89, 196802 (2002).
[35] T. Rejec and Y. Meir, Nature 442, 900 (2006).
[36] T.-M. Chen Ph.D thesis, University of Cambridge (2009)
[37] F. Sfigakis, C. J. B. Ford, M. Pepper, M. Kataoka, D. A. Ritchie, and M. Y. Simmons, Phys. Rev. Lett. 100, 026807 (2008).
[38] N. J. Craig et al., Tunable Nonlocal Spin Control in a Coupled-Quantum Dot System, Science 304, 565 (2004)
[39] M. A. Ruderman, C. Kittel, Phys. Rev. 96, 99 (1954).
[40] T. Kasuya, Prog. Theor. Phys. 16, 45 (1956).
[41] K. Yosida, Phys. Rev. 106, 893 (1957).