Investigation of electron-nuclear spin interactions in two-dimensional electron systems via magnetoresistively detected magnetic resonance.

摘要

The polarization of the electron spins and their interactions with the local nuclei are of considerable interest within two-dimensional electron systems (2DES) within the regime of the quantum Hall effect (QHE). Electron spin resonance (ESR) is an ideal experimental technique to probe both of these features. Unfortunately, due to the low electron densities, it is not usually possible to detect the ESR spectra via typical absorption techniques. However, the resonant microwave absorption by the conduction electrons may be observed as a sharp change in the magnetoresistivity within these systems, allowing for the observation of the ESR spectra via the magnetoresistive detection (MD) method.; Through the hyperfine interaction between the conduction electrons and the local nuclei, the determination of the sign of the electronic g-factor and a further understanding of the couplings present were obtained. The broadening of the ESR during slow downsweeps in magnetic field, which occurs due to the Overhauser shift of the ESR to lower field, has provided an ideal method for obtaining large nuclear polarizations within these systems. Through resonant RF irradiation of the sample, a sharp change in the Overhauser broadened MDESR spectrum is observed. This change is directly associated with the NMR excitation of the lattice nuclei and is referred to as MDENDOR spectroscopy.; The temperature dependence of the MDESR within the nu = 1 minimum was measured and allowed for the formulation of a theoretical model of the MD mechanism. This model is based on the heating of the 2DES via resonant absorption of microwaves and was utilized to provide numerical simulations of the sweep-rate dependence of the MDESR and the overall features of the MDENDOR spectra. The qualitative agreement between these simulations and the experimental measurements has provided further evidence in support of the model.; The MD method was used to observe ESR within extremely low electron density and wide parabolic quantum well samples. Both of these observations were the first of their kind. These experiments provide examples for two distinct systems where this method may be used to obtain direct measurements of the spin transitions and electron-nuclear spin interactions associated with the conduction electrons.