Laser Synchronized Optical Nuclear Magnetic Resonance via Larmor Beat Detection : Imaging Electronic Wavefunctions in Gallium Arsenide Device Structures

Citation

Miller, Michael Andrew (2001) Laser Synchronized Optical Nuclear Magnetic Resonance via Larmor Beat Detection : Imaging Electronic Wavefunctions in Gallium Arsenide Device Structures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ARCE-F837. https://resolver.caltech.edu/CaltechETD:etd-12102007-114331

Abstract

We have accomplished Optical Nuclear Magnetic Resonance (ONMR) experiments in an Al_0.36Ga_0.64As/GaAs heterojunction sample at ~2K with rf-optical pulse synchronization. The hyperfine coupling of the electron spin to the nuclear spins enable this spectroscopy in several ways, which are discussed herein. Moreover, the interactions experienced by nuclear spins in III-V semiconductors, in general, and the phenomena encountered when they are in the vicinity of a shallow donor or pseudo-donor, specifically, are developed. Furthermore, the most accurate calculation of spin diffusion in a spin-three-halves system to date is developed and presented using a methodology can be readily applied to any spin-larger-than-one-half system to a yield a set of coupled differential equations for a set of orthogonal polarizations. The behavior of these equations under a number of physical situations is also investigated.

We have captured the first ever radially resolved Knight shift images from the nuclei near a point defect in GaAs using laser synchronized ONMR. A deconvolution of these images into their constituent physical interactions has been approximately carried out using the theoretical advances developed and presented in this thesis, yielding the shape and size of the electronic orbital in which the electron is trapped, the occupancy of that electronic orbital, and the quadrupolar interactions in the vicinity of the defect, including the charge state of the defect.

Computational approaches include both full, real-time analyses of every one of the hundreds of thousands of nuclei surrounding a defect in GaAs, modeling the time domain evolution for each individual nucleus including its Knight shift, quadrupolar interactions (both secular and nonsecular), individual optical polarization conditions, optical detection weighting, and rigorously exact rf effects, and analyses of a variety of continuous medium approximations. The only computations that fit the experimental spectra are those that calculate spin diffusion along a radial line of spins, and use this approximation to the radial profile of nuclear polarization in a continuous medium approximation. The successful interface of this spin diffusion calculation and the single nucleus calculations, leveraging their individual strengths, is clearly a desirable route to further increase computational accuracy.

Thesis Files