Spin-dependent electron transport in GaAs- and InAs-based nanostructures

本项目的目的是研究低自旋轨道耦合的纳米级GaAs/AlGaAs场效应异质结（FET）中自旋相关的弹道输运，并将实验研究扩展到具有增加的自旋轨道耦合的InAs/InGaAs场效应异质结中进行直接比较。起始材料是具有高迁移率（对于GaAs基FET> 106 cm 2/Vs，对于InAs基FET>105 cm 2/Vs）的二维电子气的调制掺杂异质结构，通过电子束光刻和湿化学蚀刻从其制备Aharonov-Bohm环结构。在低温（< 4.2 K）下，四端测量了电流和电压特性随顶部电压和磁场的变化。局部纳米图案化顶栅用于控制环的电子波导中的电子密度。量子点接触具有大的子带间距（>5-10 meV），采用能量和模式过滤器和自旋极化电子的注入环计划通过使用量子点接触作为自旋过滤器元件在面内磁场。研究了注入量子点接触不同工作模式下阿哈罗诺夫-玻姆电导振荡的振幅和相位。迄今为止，量子点接触第一模式以下模式占用中的输运是用自旋相关机制讨论的，并且仍然是一个未解决的问题。其目的是调查的自旋相关的退相机制的电子量子传输，这是接近通过添加一个单电子晶体管与可调耦合的环结构。

The aim of this project is to investigate spin-dependent ballistic transport in nanoscale GaAs/AIGaAs field-effect heterostructures (FETs) of low spin-orbit coupling, and to extend the experimental studies to InAs/InGaAs field-effect heterostructures with an increased spinorbit coupling for a direct comparison. Starting materials are modulation doped heterostructures with two-dimensional electron gases of high mobilities (> 106 cm2/Vs for GaAs-based FETs and >105 cm2/Vs for InAs-based FETs) from which Aharonov-Bohm ring structures are prepared by electron-beam lithography and wet-chemical etching. Fourterminal measurements of current and voltage characteristics are taken äs a function of top voltages and magnetic fields at low temperatures (< 4.2 K). Local nanopatterned top-gates are used to control the electron densities in the electron waveguides of the ring. Quantum point contacts with large subband separations (>5-10 meV) are employed äs energy and mode filters and the injection of spin polarized electrons in the ring is planned by using a quantum point contact as spin filter element in inplane magnetic fields. The amplitude and phase of the Aharonov-Bohm conductance oscillations is investigated for different operating modes of the injecting quantum point contact. Up-to-date, the transport in the mode occupation below the first mode of a quantum point contact is discussed with spin-related mechanisms and remains an unresolved issue. The objective is the investigation of spinrelated dephasing mechanisms in the electronic quantum transport which is being approached by adding a single-electron transistor with tunable coupling to the ring structure.