Abstract
In this paper, We study the Zeeman spin-splitting in hole quantum wires oriented along the [011] and 
crystallographic axes of a high mobility undoped (100)-oriented AlGaAs/GaAs heterostructure. Our data show that the spin-splitting can be switched 'on' (finite g*) or 'off' (zero g*) by rotating the field from a parallel to a perpendicular orientation with respect to the wire, and the properties of the wire are identical for the two orientations with respect to the crystallographic axes. We also find that the g-factor in the parallel orientation decreases as the wire is narrowed. This is in contrast to electron quantum wires, where the g-factor is enhanced by exchange effects as the wire is narrowed. This is evidence for a k-dependent Zeeman splitting that arises from the spin-
nature of holes.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Spintronics aims to use an electron's spin for electronic applications. To date, the main approach to manipulating spins in semiconductors has involved using magnetic materials and interactions. However, semiconductors with a strong spin–orbit interaction present the exciting possibility of manipulating spins electrostatically. Narrow band-gap semiconductors (e.g. InGaAs) are the traditional materials for studying the spin–orbit effects. However, the emergence of GaAs hole nanodevices provides new opportunities. Because holes reside in the valence band, they have a stronger spin–orbit interaction, without the problems associated with a narrow band-gap. The spin–orbit interaction is sufficiently strong that the holes are spin-3/2 particles, leading to interesting new physics.
Main results. We have studied one-dimensional hole quantum wires fabricated on the (100) surface of an AlGaAs/GaAs heterostructure. We focus on how the Zeeman spin-splitting due to an in-plane magnetic field depends on the orientations of the field and wire relative to the semiconductor's crystallographic axes. The observed dependence is remarkably simple: with the field along the wire, we observe strong Zeeman spin-splitting, and with the field across the wire, we observe almost no Zeeman spin-splitting. This result is in stark contrast to GaAs electron quantum wires, where the Zeeman splitting is isotropic.
Wider implications. Our results highlight the interesting physics of spin-3/2 holes in GaAs, which have been relatively unexplored. A device such as this, where an energy separation between opposite spins can be switched on/off simply by rotating the magnetic field by 90° may have useful applications in spintronics.
Figure. Colour maps showing the Zeeman splitting of the one-dimensional subbands for two orientations of the wire with respect to the crystal axes and field with respect to the wire. The Zeeman spin-splitting can be switched on/off by rotating the field by 90°.