OPTICAL ORIENTATION OF SPINS IN SEMICONDUCTORS USING THE FELIX AND FELBE FREE-ELECTRON LASER FACILITIES

半导体中自旋的光学取向是利用圆偏振光子吸收的选择规则建立的一个很好的领域。利用短脉冲激光可以获得自旋动力学和控制方面的信息。该提案主要集中在窄间隙III-V半导体（NGSs），因为它们为自旋电子器件（即依赖于自旋而不是电荷的器件）提供了优势，因为它们具有高迁移率和强相对论效应，将自旋和轨道运动耦合在一起。所选择的材料具有小的带隙，这一事实立即表明，从价带到导带的自旋激发需要远红外源。此外，在这个波长范围内，人们可以在窄间隙和宽间隙材料中使用带内激发（例如掺杂样品中的传导电子）获得有关动力学的有价值的信息。如果光激发空穴影响带间实验中的电子自旋动力学，或者所研究的材料有间接间隙，则内部激发是重要的。这项提议是基于萨里大学和赫瑞瓦特大学的小组之间的合作，结合了在超快过程的红外和光学表征中使用自由电子激光（FEL）设施的经验。我们希望聘请一名来自萨里的项目学生，在FEL设施，乌得勒支FELIX和德累斯顿FELBE，研究InSb和InAs的体和量子阱（QW）结构中的自旋动力学。这项活动的一个关键方面将是培训和维护英国人员在使用FEL设施方面的专业知识，为即将到来的第四代光源（4GLS）做准备。总体的科学目标是解决与自旋操作相关的关键问题（自旋寿命和自旋弛豫）。该项目将与帝国理工学院和QinetiQ（马尔文）这两个合作机构密切合作，这两个机构将从平行资助的活动中提供一套重点系统的NGS QW结构。

Optical orientation of spins in semiconductors is a well established field that takes advantage of the selection rules for circularly polarised photon absorption. Using short pulsed lasers information can be gained on the spin dynamics and control. The proposal focusses mainly on narrow gap III-V semiconductors (NGSs) because they offer advantages for spintronic devices (i.e. devices that depend on the manipulation of spin rather than charge), due to their high mobility and strong relativistic effects that couple the spin and orbital motion. The fact that the materials of choice have small bandgap immediately indicates that far-infrared sources are required for excitation of spins from the valence band to the conduction band. In addition, in this wavelength range one can gain valuable information about dynamics using intraband excitation (e.g. of conduction electrons in doped samples) in both narrow and wide gap materials. Intraand excitation is important if e.g. photo-excited holes influence electron spin dynamics in interband experiments, or if the material under investigation has an indirect gap. This proposal is based on collaboration between groups at Surrey and Heriot-Watt Universities with combined experience in the use of Free Electron Laser (FEL) facilities in infrared and optical characterisation of ultrafast processes. We wish to hire a project student, based at Surrey, to study spin dynamics in bulk and quantum well (QW) structures of InSb and InAs at the FEL facilities, FELIX (at Utrecht) and FELBE (at Dresden). A key aspect of this activity will be the training and maintenance of expertise of UK personnel in the use of FEL facilities in preparation for the forthcoming Fourth Generation Light Source (4GLS) at Daresbury. The overall scientific objective is to resolve key issues related to spin manipulation (spin lifetime and spin relaxation). The programme will work closely with two partner institutions, Imperial College and QinetiQ (Malvern), who will provide a focused systematic set of NGS QW structures from parallel funded activities.