Spin Electronics Novel Optical Probe of Carrier Spin Coherence in Semiconductors

该提案是响应21世纪世纪自旋电子学倡议，计划征求NSF 02-036。该提案的重点是测量半导体上载流子自旋相干性的新光学技术。与传统的微电子器件相比，基于自旋的电子器件有望提供增加的处理速度、增加的集成密度和降低的功耗。此外，半导体中的电子自旋对于实现量子信息处理是有吸引力的。这些进展需要对半导体中电子自旋相干性的深刻理解，并发展探测自旋相干性的技术。先前的工作表明，n掺杂GaAs具有非常长的自旋相干时间，这促使了进一步的研究。半磁半导体的自旋相干性要短得多，但载流子-离子相互作用较强，使其成为制备自旋滤波器和相关器件的较好候选材料。本项目开发的技术将补充法拉第旋转的主导技术，并提供使用法拉第旋转无法获得的信息。特别感兴趣的是为什么法拉第旋转信号对于高光激发密度饱和。该技术是基于瞬态四波混频。具体地，通过使用三脉冲激发方案，可以探测自旋相干性并在背景自由方向上产生信号。使用五阶非线性光学响应的对此的修改可以生成拉曼自旋回波，这将消除例如由于g因子随k矢量的变化而引起的不均匀自旋进动速率的影响。实验将在n掺杂GaAs和半磁半导体如CdMnTe和ZnMnTe上进行。前者样品为市售晶圆，后者将由德国多特蒙德大学的合作者提供。在后一种情况下，将进行初步实验，以探测光学相干性（相对于自旋相干性），因为它还没有得到很好的理解，并提供了重要的洞察载流子离子自旋散射，这是至关重要的电子控制铁磁性。初步的法拉第旋转实验将在GaAs和半磁性半导体样品上进行，以提供与其他小组实验结果的联系。在此期间，自旋相干和拉曼自旋回波实验将在n掺杂GaAs上进行。对于半磁性半导体，将进行光学相干和自旋相干实验。

This proposal was received in response to the Spin Electronics for the 21st century initiative, Program Solicitation NSF 02-036. The proposal focuses on novel optical techniques for measuring carrier spin coherence on semiconductors. Spin based electronics promise to provide increased processing speed, increased integration density and decreased power consumption as compared to traditional microelectronic devices. In addition, electronic spins in semiconductors are attractive for implementation of quantum information processing. These advances require a firm understanding of electronic spin coherence in semiconductors and the development of techniques to probe spin coherence. Previous work has shown that n-doped GaAs has a remarkably long spin coherence time, which has prompted further investigation. Semimagnetic semiconductors display much shorter spin coherences, however the stronger carrier-ion interaction makes them better candidate materials for fabrication of spin filters and related devices.The techniques developed in this project will complement the predominant technique of Faraday rotation and provide information that is not available using Faraday rotation. Of specific interest is why the Faraday rotation signal saturates for high optical excitation density. The techniques are based on transient four-wave-mixing. Specifically, by using a three pulse excitation scheme, it is possible to probe the spin coherence and generate a signal in a background free direction. A modification of this that uses the fifth order nonlinear optical response can generate a Raman-spin echo, which will remove the effects of inhomogeneous spin precession rates due, for example, to a variation in the g-factor with k-vector. The experiments will be performed on n-doped GaAs and semimagnetic semiconductors such as CdMnTe and ZnMnTe. The former samples are commercially available wafers, while the latter will be provided by collaborators at the University of Dortmund, Germany. In the latter case, initial experiments to probe the optical coherence (as opposed to spin coherence) will be performed because it is not well understood and provides important insight into carrier-ion spin scattering, which is crucial for electronically controlled ferromagnetism. Preliminary Faraday-rotation experiments will be performed on both the GaAs and semimagnetic semiconductor samples to provide a connection to experimental results from other groups. During this grant, both spin-coherence and Raman-spin echo experiments will be performed on n-doped GaAs. For the semimagnetic semiconductors, optical coherence and spin coherence experiments will be performed.