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Spin Dephasing Anisotropy in Bulk Gallium Arsenide

Zwier, O.V. (2012) Spin Dephasing Anisotropy in Bulk Gallium Arsenide. Master's Thesis / Essay, Physics.

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In the first part of this thesis, the origins of Spin Dephasing Anisotropy (SDA) in semiconductors are discussed, to pave the way for a design and realization of a device, meant to characterize SDA in two-dimensional and bulk electron gasses in GaAs. The anisotropy will be investigated in quasi-ballistic channels, oriented in four different crystallographic directions. Due to the nature of the Spin-Orbit fields (SO-fields) in the material, a strong dependency of SDA on channel orientation is expected. Passing currents through these channels, applying external magnetic fields, and top gating are all possible in situ, to analyze their expected effects on the SDA. The fabrication was not fully completed at the time of writing, but the most crucial step of wet etching micrometer-sized structures had been fully characterized and perfected, and the remaining steps had been tested for, leaving very little work yet to be completed. To support these and previous measurements on bulk electron gas measurements, the second part of this thesis presents a numerical study of the electron spin dephasing time $T_2^*$ in quasi-ballistic wires of bulk GaAs material. The study assumes that dephasing occurs due to spin-orbit fields from a bulk Dresselhaus term and a Rashba term in wires with either specular or non-specular momentum scattering on the walls of the wire. With a similar magnitude for the Dresselhaus and Rashba effect our results show the longest $T_2^*$ values for wires in [110] direction. This is consistent with the dependence of $T_2^*$ on the crystal orientation of wires that was observed in recent experiments. However, a comparison with results for random momentum scattering on the wire edges reveals that the mechanism behind the spin dephasing anisotropy differs from the analogues effect in wires with two-dimensional electron systems: instead of a confinement-induced motional-narrowing effect, spin dephasing anisotropy now results from the interplay between repetitive electron trajectories in the wire and the anisotropy in the spin orbit fields. This points to a mechanism that has similarities with the phenomenon of ballistic spin resonance that can occur in wires based on 2D electron systems. A large part of the simulations also concerned studying the magnetic field dependence of this phenomenon with simulations that account for the field-induced cyclotron motion of electrons.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Physics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:47
Last Modified: 15 Feb 2018 07:47

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