双子带量子阱的自旋漂移扩散
Spin drift-diffusion for two-subband quantum wells
摘要：
控制自旋动力学和自旋寿命是自旋电子学的主要挑战之一。为此，在二维电子气（2DEG）的自旋扩散的研究表明，当Rashba和Dresselhaus自旋轨道耦合（SOC）是平衡的，一个持久的自旋螺旋制度出现。在那里，条纹自旋模式显示出很长的寿命，仅受立方Dresselhaus SOC的限制，并且其动力学可以由面内漂移场控制。在这里，我们推导出一个自旋扩散方程的非简并两个子带2DEG。结果表明，由子带密度重叠定义的子带间散射率作为控制自旋动力学的一个新的参数，可以由电场控制，并且在对称量子阱中最大.我们发现，对于大的子带间耦合的动态遵循一个有效的扩散矩阵的子带平均矩阵的约一半。这个额外的1/2因子来自于Matthiessen规则对子带内和子带间散射率的求和，并且导致降低的扩散常数和较大的自旋寿命。我们说明了我们的研究结果与数值解的扩散方程的参数从现实的薛定谔-泊松计算。
英文摘要：
Controlling the spin dynamics and spin lifetimes is one of the main challenges in spintronics. To this end, the study of the spin diffusion in two-dimensional electron gases (2DEGs) shows that when the Rashba and Dresselhaus spin-orbit couplings (SOC) are balanced, a persistent spin helix regime arises. There, a striped spin pattern shows a long lifetime, limited only by the cubic Dresselhaus SOC, and its dynamics can be controlled by in-plane drift fields. Here, we derive a spin diffusion equation for non-degenerate two-subbands 2DEGs. We show that the intersubband scattering rate, which is defined by the overlap of the subband densities, enters as a new nob to control the spin dynamics, and can be controlled by electric fields, being maximum for symmetric quantum wells. We find that for large intersubband couplings the dynamics follow an effective diffusion matrix given by approximately half of the subband-averaged matrices. This extra 1/2 factor arises from Matthiessen's rule summing over the intra- and intersubband scattering rates, and leads to a reduced diffusion constant and larger spin lifetimes. We illustrate our findings with numerical solutions of the diffusion equation with parameters extracted from realistic Schrödinger-Poisson calculations.
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