RUI: Measurement of Density of States of (Ga,Mn)As and Diffusion of Photoinduced Order by Ultrafast Transient-Grating Spectroscopy

****技术摘要****(Ga,Mn)As是III-V稀释磁性半导体（DMS）中研究最多的一种。这些材料通过对其磁性的光学和电气控制提供了可能的自旋电子应用，但实际应用需要设计居里温度高于室温的新材料。爱因斯坦关系允许人们根据电阻率和空穴扩散系数的测量，独立于空穴密度，找到费米能级（DOS）上的态密度。本项目将使用超快光学测量孔扩散系数，从而确定DOS。实验将瞬态光栅光谱应用于（Ga,Mn）As，从而测量自旋扩散和双极性扩散；这两个反过来，给出了孔洞的扩散。这些测量可以区分（Ga,Mn）As中孔的广泛支持的价带和杂质带图像。由于空穴介导磁交换，因此对其性质的争论是理解DMS的基础，而更好的理解可以帮助开发新的DMS材料。本科生将参与项目的每一部分。他们将学习超快激光、光学对准、数据分析、磁学、半导体物理和光谱学。这段经历将使他们为各种各样的职业和研究生项目做好准备。****非技术摘要****稀释磁性半导体（DMS）在“掺杂”少量杂质时变得具有磁性。磁性半导体可以用于许多被提议的设备，包括非易失性晶体管，这将大大降低计算机的功耗，但实际应用将需要设计在室温下工作的新型DMS材料，而不是目前材料的零下温度。由于缺乏对DMS如何变成磁性的理论理解，对这种材料的研究一直受到阻碍。GaMnAs是一种典型的DMS，但对于使其具有磁性的电子过程，特别是控制其磁性的“孔”的移动程度，存在尖锐的分歧。该项目将使用脉冲短于十万亿分之一秒的超快激光器来测量孔的迁移率，从而提高对DMS的理解。该项目还将研究一种相关的现象，目前人们对这种现象知之甚少，即暴露在光线下会增强伽马胺的磁性。本科生将参与项目的每一部分，为实验的进步做出贡献，并接受实验物理方面的训练。他们将学习使用超快激光器，非常擅长光学校准，并熟悉磁学，半导体物理和光谱学。由于这些主题的科学和工业相关性，以及超快技术的快速发展，学生将为各种各样的职业和研究生课程做好准备。

****Technical Abstract****(Ga,Mn)As is the best-studied of the III-V dilute magnetic semiconductors (DMS). These materials offer possible spintronic applications through the optical and electrical control of their magnetic properties, but practical application awaits the design of new materials with Curie temperature above room temperature. The Einstein relation allows one to find the density of states at the Fermi level (DOS) based on measurements of the resistivity and the hole diffusion coefficient, independent of hole density. This project will use ultrafast optics to measure the hole diffusion coefficient, and thereby determine the DOS. The experiment will apply transient-grating spectroscopy to (Ga,Mn)As, thus measuring the spin diffusion and the ambipolar diffusion; these two in turn, give the hole diffusion. These measurements could distinguish between the widely supported valence-band and impurity-band pictures of holes in (Ga,Mn)As. Since the holes mediate magnetic exchange, the debate over their properties is fundamental to understanding DMS's, and improved understanding could aid the development of new DMS materials. Undergraduate students will participate in every part of the project. They will learn about ultrafast lasers, optical alignment, data analysis, magnetism, semiconductor physics, and spectroscopy. The experience will prepare them for a wide variety of careers and graduate programs.****Non-Technical Abstract****The dilute magnetic semiconductors (DMS's) become magnetic when they are "doped" with small quantities of impurities. Magnetic semiconductors could be used in many proposed devices, including nonvolatile transistors that would dramatically reduce computers' power consumption, but practical use will require the design of new DMS materials that operate at room temperature, rather than the subzero temperatures of current materials. The search for such materials has suffered from a lack of theoretical understanding of how a DMS becomes magnetic. GaMnAs is an archetypal DMS, but there is sharp disagreement over the electronic processes that make it magnetic, particularly over how mobile the "holes" are that control its magnetism. This project will use ultrafast lasers, with pulses shorter than one ten-trillionth of a second, to measure the holes' mobility, providing an improved understanding of DMS's. The project will also investigate a related phenomenon, as yet poorly understood, in which exposure to light strengthens the magnetism of GaMnAs. Undergraduate students will participate in every part of the project, contributing to experimental progress and being trained in experimental physics. They will learn to use ultrafast lasers, get very good at optical alignment, and become familiar with magnetism, semiconductor physics, and spectroscopy. Because of the scientific and industrial relevance of these topics, and the rapid growth of ultrafast technology, the students will be prepared for a wide variety of careers and graduate programs.