自旋流线性电光效应研究

Spintronics is one of new branches in physics that grew rapidly these years. Different from traditional electronics, which studies the storing, processing and transferring of information based on the character of electron having charge, spintronics investigates how to realize the same aim of information application by means of the spins with electrons. The transmission of information carried by the spins of electrons depends on the spin currents. And the key step for the utilization of this information is to realize the exploration of these spin currents. On the other hand, spin currents are found to be closely related to the new phenomena of physics discovered these years, for example, the phenomena of topological insulators and the Spin Hall Effect. So it is important and significant not only for the practical applications but also for the foundational physics for us to realize the exploration of spin currents. It is known that the spin currents will induce nonzero the second order nonlinear susceptibilities in the materials carrying these spin currents. We note that these induced nonzero the second order nonlinear susceptibilities can support not only the processes of double frequency,sum frequency and difference frequency, but also the Pockels effect. This project presents a proposal to investigate the Pockels effect of spin currents and further searches after the principle and method for the exploration of spin currents based on Pockels effect. The exploration of spin currents based on Pockels effect is with much higher potential than those methods based on other nonlinear optical principles since it needs only very low beam intensity, which can availably avoid the thermal effect of light.

自旋电子学是近年迅速发展起来的物理学新兴学科。传统电子学着眼于利用电子带电这一物理特性实现信息的存储、处理和传输，而自旋电子学则致力于研究利用电子的自旋来实现相关的功能。电子自旋信息的传输依赖于自旋流。而要实现电子自旋流信息的应用，关键的一步是实现自旋流的探测。另一方面，自旋流还与近年发现的新奇物理现象, 如拓扑绝缘体和自旋霍尔效应等密切相关，所以自旋流探测无论在基础物理还是在实际应用方面都具有重要的意义。自旋流会在传导材料中诱导出非零二阶非线性电极化率。我们注意到，这些非零的二阶非线性电极化率，不仅可以支持倍频、和频、差频等光学混频过程，而且在一定条件下也能导致 Pockels 效应即线性电光效应。据此，本项目提出研究自旋流线性电光效应，探索利用线性电光效应探测自旋流的原理和方法。用线性电光效应探测自旋流与用其它非线性光学方法不同，能用很弱探测光，因此可避免热效应，更具应用潜力

我们从理论上预言自旋流可诱导线性电光效应，并根据自旋流诱导的附加线性电极化率和线性电光效应的耦合波理论，提出基于线性电光效应直接测量自旋流的方案。例如对n掺杂GaAs晶体中的自旋流的直接测量，当探测光的频率为1.5 eV、外加电场强度为350 V/mm，n掺杂GaAs晶体的厚度为3 um时，大小为20 nA/um^2的横向自旋流造成的探测光的偏振转角为14.1 urad；大小为20 nA/um^2的纵向自旋流造成的探测光的偏振转角可达28 urad。这以现有的实验技术完全可以观测到。我们还发现吸收效应对利用线性电光效应测量自旋流会产生明显影响。在共振吸收带附近，探测光的吸收效应最大可引起10%的测量误差。为了深入研究自旋流的线性电光效应，我们进一步研究非局域线性电光效应，由此提出一个可用于入射光方向任意、外加电场方向任意，对各种点群对称性晶体都适用的非局域线性电光效应耦合波理论。因为自旋流调控联系到光角动量和光力问题，我们研究了相关课题。