All-Electric Semiconductor Spin Valve

提出了一种大导通比（~ 30）的全电动横向旋转阀的实验和理论研究方案。该装置将由砷化镓制成，不使用任何铁磁电极或外部磁场来翻转电子自旋。它由两个量子点串联组成，由一个短的一维传导通道隔开，该通道的长度小于砷化镓在工作温度下的自旋相干长度。每个量子点接触充当全电自旋极化器或探测器，可以提供或过滤几乎完全自旋极化的电流。模型器件的非平衡格林函数仿真表明，基于砷化镓量子点接触的自旋阀器件在现代光刻技术下可实现数十纳米长度尺度的自旋分裂，可以产生足够大的自旋分裂，在室温下具有大的导断比。在半导体自旋电子学中，用纯电的方法产生、操纵和检测自旋极化电流是具有挑战性的目标。迄今为止研究的自旋阀使用铁磁电极或嵌入到器件结构中的材料来进行自旋极化和检测，并使用外部磁场来翻转自旋。最近，我们已经证明了由半导体砷化铟制成的量子点接触可以通过纯电手段产生强烈的自旋极化电流，当其限制势被门偏置电压高度不对称时。本项目将开发的基于砷化镓量子点接触的自旋阀在两个方面是独特的。首先，将全电量子点接触用作自旋偏振器和探测器。其次，使用一维传输通道，与目前使用的二维通道相比，它具有许多优点。最后，由于在室温下砷化镓的自旋相干长度（几十微米）相对于砷化铟的自旋相干长度（几十纳米）较长，砷化镓自旋阀在室温下运行是可行的。如果成功，这个项目将是开创性的。更广泛的影响该项目的成功有望刺激全电动、超高速、节能自旋阀设备的发展，这些设备可用于高速数字信息处理，并最终用于基于自旋量子比特的固态量子计算。这个项目如果成功，将是半导体自旋电子学的一个重要里程碑和突破。该项目的目标是开发第一个基于非平衡格林函数技术的模拟器，以模拟纳米级器件中的自旋输运，并通过nanoHUB网站向科学界提供。研究生和本科生都将参与这项研究工作。该项目将特别吸引泽维尔大学和辛辛那提大学的本科物理/工程专业学生参与传统本科课程和课程中无法获得的前沿物理研究和先进技术。

A concerted experimental and theoretical research program is proposed to develop an all-electric, lateral spin valve with a large (~ 30) On/Off conductance ratio. The device will be made from gallium arsenide and will not use any ferromagnetic electrodes or external magnetic field to flip the electron spin. It consists of two quantum point contacts in series separated by a short one-dimensional conduction channel of length smaller than the spin coherence length of gallium arsenide at the temperature of operation. Each quantum point contact acts as all-electric spin polarizer or detector and can provide or filter almost completely spin-polarized current. Non-equilibrium Green¡¦s function simulation of model devices indicate that spin valve devices based on gallium arsenide quantum point contacts on length scale of tens of nanometers, achievable with modern lithographic technology, can yield a large enough spin splitting to make feasible operation at ambient temperature with large On/Off conductance ratio.Intellectual meritThe creation, manipulation, and detection of spin-polarized currents by purely electrical means are challenging goals in semiconductor spintronics. Spin valves so far studied have used ferromagnetic electrodes or material embedded into device architecture for spin polarization and detection and an external magnetic field to flip the spin. Very recently, we have demonstrated that quantum point contact made from the semiconductor indium arsenide can be used to generate strongly spin polarized current by purely electrical means when its confining potential is made highly asymmetric by gate bias voltages. The spin valves based on gallium arsenide quantum point contacts we will develop in this project are unique in two respects. First, all-electric quantum point contacts will be used as spin polarizer and detector. Second, a one-dimensional transport channel is used that offers a number of advantages over two-dimensional channels used so far. Finally, because of the long (tens of micrometers) spin coherence length of gallium arsenide relative to that (tens of nanometers) of indium arsenide at room temperature, operation of the gallium arsenide spin valves at ambient temperature is feasible. If successful, this project will be ground-breaking. Broader ImpactsThe success of this project is expected to stimulate the development of all-electric, ultra high-speed, energy-efficient spin valve devices that can be used for high-speed digital information processing and eventually in solid-state quantum computation based on spin qubits. This project, if successful, will be a major milestone and a breakthrough in semiconductor spintronics. A goal of this project is to develop the first simulator based on non-equilibrium Green¡¦s function technique to model spin transport in nanoscale devices and make it available to the scientific community at large via the nanoHUB website. Both graduate and undergraduate students will participate in this research effort. This project will specifically engage undergraduate physics/engineering students of Xavier University and the University of Cincinnati to cutting edge physics research and advanced techniques not accessible in traditional undergraduate programs and courses.