閘極局域的開放式量子點與一維通道的抽運傳輸,整流,與自旋極化機制

Abstract

我們將繼續之前在奈米結構的量子電荷抽運與整流傳輸機制的研究，我們有興趣 的奈米結構是閘極局域的開放式量子點與量子窄通道，再者，我們會探討奈米結構系 統的自旋極化物理；過去數年，我們已建立一套電子束微影技術，並成功地在砷化鎵 異質結構上製作各式奈米尺度的表面閘極，此高mobility 的二維電子氣乃由以色列 Weizmann 研究中心的Umansky 博士研究小組提供，開放式量子點可藉由兩高頻但具 相位差的局域位能造成量子系統在無外加DC 偏壓下產生DC 電流，此抽運的測量技術 已建構完成，（目前頻率可達80MHz），而且我們目前初步的實驗證實了量子抽運電流 在我們元件內的存在，由於閘極的對稱性安排，抵銷了整流電流。為了更確定這幾何 安排的效應並進而更瞭解此二機制，我們將設計不同RF 閘極組態，觀察dc 電流，釐 清二者的相對貢獻，同時我們將針對抽運電流與量子點物性（尺寸大小、能態）做深 入探討；另外，我們將著重於窄通道的量子電荷抽運機制，並提高頻率範疇，多組指 狀閘極對將直接製作於窄通道之上，由指狀閘極幾何上的不同安排，可更深入認識抽 運機制；最後，我們將研究複合式奈米結構的傳輸機制，量子點的電荷抽運在適量的 Zeeman 分裂下將可成為相位同調的自旋抽運，組合量子點與量子尖端接點可形成自旋 極化電流源與偵測器，我們將研究自旋軌道作用在自旋鬆弛與非同調性的扮演角色。

In all, we propose to continue our studies in quantum charge pumping and rectification transport properties within nanostructures. Nanostructures that we are interested in are gate-confined quantum dots and one dimensional narrow channels. Moreover, spin polarization in nanostructures will also be explored. We have been successfully set up e-beam lithography that allows us to make different arrangements of surface gates atop GaAs-based 2DEG. The high mobility GaAlAs/GaAs heterostructures are provided by Dr. Umansky at the Weizmann Institute in Israel. The measurement for DC pumped current induced by two confining potentials with the same frequency (up to 80MHz) but a phase difference (0~2釘) has also well established. Earlier work provides evidence that we have observed quantum charge pumping in open quantum dots. The alleviation of rectification current in our devices is attributed to geometrical symmetry of gate arrangement. However, there are many interesting and important properties required to be further investigated. For instance, the influence of the gate arrangement on both quantum pumping and rectification mechanisms is one issue. The impact of dot properties such as dot size, number of electrons, energy level spacing,.. etc. on quantum charge pumping is another critical issue. Then, we expect to promote our technique with frequency up to 40GHz and focus on the quantum charge pumping in narrow channels. Finger gate array will be fabricated on the top of a narrow channel. It has also been known that a quantum-dot based charge pump in the presence of sizable Zeeman splitting would function as a phase-coherent spin pump. Combination of a quantum dot and a quantum point contact can act as a spin-polarized current generator and detector. The role of spin-orbit interaction in spin relaxation and decoherence will be explored.