自旋，作為粒子的一個本徵量子數，引發了許多科學家的興趣因為它無法以古典物理的概念來理解。雖然自旋已被廣泛的研究，但是其在電子元件方面的應用上依然存在著挑戰：要產生不同自旋之間的能量差，一個強磁場的操控是必要條件，然而這是非常不切實際的。令人驚訝的是，在一個有著顯著的自旋軌道交互作用的系統中，當粒子的運動方向垂直於一電場時，粒子的自旋將與其動量耦合，產生一個等效磁場。因此，自旋將能以電性的方式被操控，相較於磁場的方式更加便利。
在本篇論文中，我們證明了量子點接觸的自旋選擇性並發展一個量測自旋軌道交互作用強度的新技術，此交互作用有著利用電性方法控制電子自旋，並以此為基礎實現相關應用的潛在價值。在我們的實驗中，由於Rashba自旋軌道交互作用的存在，帶有兩種不同自旋的電子流在空間中被微弱的垂直磁場分離，這一空間上的分離讓我們得以研究量子點接觸的自旋選擇性。由於元件的幾何結構小於電子動量弛豫的平均自由徑，量子態將同調地隨時間演化，我們觀察到了電子的自旋進動，藉此提取出以頂電極電壓為函數的自旋軌道交互作用強度。

Spin, an intrinsic quantum number of particles, attracts lots of interest from scientists as it is a remarkable property that cannot be understood in classical physics. Although the spin has been investigated extensively, there remains a challenge to utilize spin for electronic application: one has to apply and vary a large magnetic field to create the energy difference between opposite spins, which is extremely impractical. Amazingly, in mesoscopic systems with strong spin-orbit interaction, particles’ spin are coupled to their momentum, resulting in the appearance of an effective magnetic field when the particles are travelling perpendicular to an electric field. Thus, the spins could be manipulated in an electrical manner which is much more convenient than the magnetic counterpart. In this thesis, we demonstrate the spin selectivity of the quantum point contacts and develop a new technique to detect the strength of spin-orbit interaction, which may hold the key to realize spin-based applications by electrical means. In our experiment, the two spin currents with different spin orientation are spatially separated by a weak transverse magnetic field due to the Rashba spin-orbit coupling. This spatially separation of the spin currents allows us to investigate the spin selectivity of the quantum point contact. Because the device geometry is smaller than the mean free path for momentum relaxation, the time evolution of the quantum states are coherent and the spin precession is observed, the strength of the spin-orbit interaction as a function of top-gate voltage is therefore extracted.

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