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Embargoed until 2016-09-30
Copyright: Srinivasan, Ashwin
Embargoed until 2016-09-30
Copyright: Srinivasan, Ashwin
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Abstract
Quantum confined holes in GaAs offer the possibility of electrical spin manipulation via the spin-orbit interaction for the development of spintronic devices. This is a newly developing area of research, and there remain many open questions and further theoretical and experimental investigations are needed for a complete understanding of hole spins. The specific focus of this investigation is to study the g-factor anisotropy of hole systems and the effects of the 2D confinement potential and Rashba interaction.
Firstly, we measure the g-factor perpendicular to the 2D hole plane using a quantum point contact (QPC) fabricated on a (100) GaAs/AlGaAs heterostructure. The out-of-plane g-factor g_zz has been theoretically predicted to be 7.2, but this long standing theory has yet to be experimentally verified. We find an increasing g-factor as a function of subband index n, with g_zz = 5 at n = 5 when the channel is widest, approaching the theoretical 2D limit of 7.2.
Secondly, we study Zeeman splitting of a hole QPC fabricated on a (311) GaAs/AlGaAs heterostructure. Unlike (100) GaAs, the crystallographic anisotropy of the (311) plane results in unusual effects such as anisotropy of the 2D g-factor in the plane. Furthermore, it has been predicted that applying a field along [2b33] results in an anomalous out-of-plane polarisation. Here we use combined magnetic fields applied along [311] and [2b33] to provide the first experimental confirmation of this intriguing prediction. We also observe evidence for anti-crossing behaviour as well as a sign reversal of the in-plane g-factor g_[2b33].
Finally, we study the effects of 2D confinement potential and the Rashba interaction on the 1D g-factor. This experiment is carried out on 1D hole channels fabricated from two heterostructures: i) a single heterojunction (SHJ) and ii) a quantum well (QW) with tuneable electric field. We measure a very large in-plane g-factor anisotropy (g_pll/g_perp) for the SHJ device, which features a strong Rasha interaction, but a small anisotropy for the QW device when the Rashba interaction is tuned to a minimum. We have demonstrated electrical tuning of the g-factor, which is of interest for spintronics applications.