摘要

此論文主要發展近藤效應(Kondo effect)的非局域性操控。而在量子點這種的封閉系統中可以抓住電子自旋，利用此特性可以觀察到兩個重要的物理現象為近藤效應以及非尋常零偏壓效應(Zero bias anomaly)。在兩個量子點的系統中，N. J. Craig發現可以藉由改變一邊量子點的電子數目來去影響另一邊量子點的近藤效應 [1]。此現象發生的原因為近藤效應以及RKKY作用互相影響 [2]。Cronenwett指出除了量子點以外，在量子線這種開放式系統照理說沒有束縛態可抓電子自旋，竟然也發現有關於近藤效應的特徵。
以上這些研究激勵我們的想法，我們設計出一個嶄新的量子元件，其構造為一個耦合系統由量子點以及量子線組合而成。為了了解量子點的電子數目，會去測量庫倫阻擋效應(Coulomb blockade)。之後應用偏壓來去測量在量子線中非尋常零偏壓效應當量子點的電子數目為偶數以及奇數的情況下。最後，進一步的去使用外加磁場觀察量子線的零偏壓效應有何變化。

Abstract

The project of this thesis is to develop a non-local control of Kondo effect. The Kondo effect and zero basis anomaly (ZBA) are important phenomen in the quantum dot (QD), which is a closed system and can trap spin. According to the research of double QDs system performed by N. J. Craig et al[1], the ZBA of a dot in Kondo regime can be remotely controlled and split by tuning the number of electrons and coupling of an adjacent QD. The phenomenon is due to the competition between Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction[2]. In addition to QD, quantum point contact (QPC), an open system wherein in principle no localized state should occur, were recently linked to Kondo physics by Cronenwett et al[3].
We are inspired by these researches and conceive an integrated quantum device, wherein a QD is coupled with a QPC. To understand of the number of electrons inside the dot, we measure the Coulomb blockade spectrum. Then, we apply a source-drain bias to measure the ZBA in the QPC at various states when QD contains odd or even number of electrons. Furthermore, we apply an external magnetic field to measure the ZBA variation in QPC.
Our experimental data demonstrates encouraging results that we can successfully and accurately control the Kondo feature, ZBA, in QPC by tuning the number of electrons in the QD. However, by applying an external magnetic field parallel to the channel, the zero bias peak is not split. The result presented in this thesis facilitate us to understand the cause of zero bias peak in QPC and develop a method for remote spin control.

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