Band Structure and Transport in Low-Dimensional Semiconductor Hole Systems

• Applicant: Dr. Paul Thomas Wenk
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 336985961

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.

• DFG Programme: Research Grants
• International Connection: Mexico
• Co-Investigator: Professor Dr. John Schliemann
• Cooperation Partners: Professor Dr. Dominique Bougeard; Professor Dr. Francisco Mireles Higuera; Professor Dr. Klaus Richter