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的自旋-轨道耦合(SOC)产生了极大的兴趣。本项目特别侧重于孔系统，其特殊之处有几个原因。一方面，与导带电子相比，空穴的有效质量较大，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可能更强大。另一方面，重空穴(HH)态和轻空穴(LH态)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。这允许较长的自旋弛豫(SR)/退相时间。所有这些特征都有助于非常有效地操纵载体自转。这项提议是关于研究p型系统的不同具有挑战性的方面。其一是应变闪锌矿(ZB)型和纤锌矿(WZ)型孔系中载流子的SR分析。我们的目标是在构建自旋电子学应用方面使这种SR最小化，甚至找到持久的自旋态。最近，我们证明了2DZB电子系统中存在持久的自旋螺旋，并给出了半导体异质结一般生长方向所需的条件。受这一发现的启发，我们想要回答这样一个问题，在生长方向不是[001]的系统中，是否也存在2D空穴气体(2DHG)中的自旋保持对称性。随机共振的分析直接与这种2DHG的导电性质有关，这将通过计算弱(反)局域化(WL/WAL)来实现。WL/WAL已被证明是在实验中探测SOC的重要工具之一。该分析将考虑SO场的完全对称性，这超出了Pikus等人的理论。或Iordanskii等人。为了清楚地了解WL/WAL和SR之间的联系，必须研究磁导性。这将我们带到这个项目中要回答的下一个不平凡的问题，即如果我们考虑SOC效应和禁闭，塞曼项中的有效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，因此考虑应变效应是很重要的，应变效应显著地影响了能带间距。进一步的工作方向包括研究洞系统中的Zitterbewegung，包括2DHG的应变和线性Dresselhaus SOC项，这些项到目前为止一直被忽略，但最近被证明是重要的。波包动力学将在真实的样本几何体中模拟。正如Durnev等人最近所表明的那样，所开发的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。

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.