Band Structure and Transport in Low-Dimensional Semiconductor Hole Systems

在过去的几年里，人们对二维半导体系统中自旋轨道耦合（SOC）产生了极大的兴趣。本项目特别关注由于几个原因而具有特殊性的孔系统。一方面，与导带电子相比，空穴的有效质量更大，从而减小了动力学项，使得SOC的贡献变得更加重要；因此，与n型系统相比，SOC可以更强。另一方面，重空穴（HH）和轻空穴（LH）态的p波特性降低了载流子自旋与原子核的超精细相互作用。这允许长自旋弛豫(SR)/消相时间。所有这些特征都有助于非常有效地操纵载流子自旋。这个提议是关于研究p型系统的不同的具有挑战性的方面。其中一项是分析了应变锌-闪锌矿（ZB）型和纤锌矿（WZ）型孔洞体系中载体的SR。在构建自旋电子学应用方面，目标是最小化这个SR，甚至找到持久的自旋状态。最近，我们证明了二维ZB电子系统中持续自旋螺旋的存在，并提供了半导体异质结构大多数一般生长方向所需的条件。受这一发现的启发，我们想要回答这个问题，即2D空穴气体（2DHG）中的自旋保持对称性是否也出现在除[001]以外的生长方向的系统中。SR的分析与这种2DHG的传导特性直接相关，这将通过计算弱（反）局域化（WL/WAL）来接近。在实验中，WL/WAL已被证明是探测SOC的重要工具。分析将考虑到SO场的完全对称性，超越Pikus等人或Iordanskii等人的理论。为了清楚地了解WL/WAL和SR之间的联系，必须研究磁导率。这就引出了我们在这个项目中要回答的下一个重要问题，即，如果我们考虑SOC效应和约束，塞曼术语中的有效g因子是什么样子的。此外，由于g因子强烈依赖于HH-LH子带分裂，因此考虑应变效应非常重要，应变效应会显著影响能量间隔。进一步的工作方向包括研究井系统中的zitterbeweung，包括k Dresselhaus SOC中的应变和线性2DHG，迄今为止被忽视，但最近已被证明是重要的。波包动力学将模拟在现实的样品几何。将使用的开发模型还将考虑异质结构界面，这可能导致HH自旋分裂的主要贡献，正如Durnev等人最近所表明的那样。

The past years have witnessed an enormously increasing interest regarding spin-orbit coupling (SOC) in two-dimensional (2D) semiconductor systems. The present project focuses in particular on hole-systems which are special for several reasons. On the one hand, the large effective mass of holes compared to conduction band electrons diminishes the kinetic term such that contributions from SOC become more important; thereby, the SOC can be strong compared to n-type systems. On the other hand, the p-wave character of the heavy (HH) and light hole (LH) states reduces the hyperfine interaction of the carrier spin with the nuclei. This allows for long spin relaxation(SR)/dephasing times. All these features facilitate a very effective manipulation of carrier spins. This proposal is about studying different challenging aspects of p-type systems. One of them is the analysis of SR of carries in strained zinc-blende (ZB) type and wurtzite (WZ) type hole system. The goal is to minimize this SR or even find persistent spin states, in respect of building spintronics applications. Recently, we supplied proof for the existence of a persistent spin helix and the needed conditions in 2D ZB electron systems for most general growth directions of the semiconductor heterostructure. Inspired by this findings, we would like to answer the question, whether spin preserving symmetries in 2D hole gases (2DHG) also arise in systems with growth directions other than [001]. The analysis of SR is directly linked to the conduction properties in such a 2DHG which will be approached by calculating weak (anti)localization (WL/WAL). The WL/WAL has proved to be one important tool for probing SOC in experiments. The analysis will take into account the full symmetry of the SO field, going beyond the theory by Pikus et al. or Iordanskii et al. To have a clear understanding of the link between WL/WAL and SR, magnetoconductivity has to be studied. This brings us to the next nontrivial question to be answered in this project, namely, how the effective g-factor in the Zeeman term looks like if we consider SOC effects and confinement. Furthermore, since the g-factor strongly depends on the HH-LH subband splitting, it is important to comprise strain effects, which significantly influence the energy spacing. Further directions of work include the study of Zitterbewegung in hole systems including strain and linear in k Dresselhaus SOC terms for the 2DHG which have been neglected so far but have been shown recently to be significant. The wave packet dynamics will be simulated in realistic sample geometries. The developed models to be used will also take account of heterostructure interfaces which can cause dominant contributions to HH spin splitting as recently shown by Durnev et al.