Quantum Transport and the Aharonov-Casher Effect in Two Dimensional Electron Gases

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The objective of this research is to show experimentally that the phase of the electron spin in a two dimensional electron gas can be manipulated to produce quantum interference effects modulating the electrical conductivity; this effect was predicted by Aharonov and Casher in 1984. With the atomic strength electric fields present in zincblende semiconductors, the Aharonov-Casher interference should be observable using the electron magnetic moment in a two dimensionally confined electron gas. The induced phase shift is predicted to be 2-10 pi radians for realizable mesoscopic geometries. Ring geometries and Young interferometers will be defined on GsAs heterojunction field effect devices. The phase will be varied through the dependence of the electron magnetic moment upon electron surface density. In zero magnetic field the observation of oscillations in the electron conductivity, periodic in surface electron density and of magnitude 1/(25812) mhos, will demonstrate the validity of the Aharonov-Casher approach to the understanding of the spin dependent properties of mesoscopic systems. These experiments will be essential for predicting the role that electron spin plays in quantum dot and ballistic transport experiments implemented in semiconductor heterojunctions. %%% The principles of electron transport in semiconducting solids have been understood for a long time. In the last decade, interference effects illustrative of the wavenature of the electron have been observed when very small device structures are made. These sizes need to be of the order of the electron wavelength, about one ten millionth of a meter. The fabrication technology for these quantum devices originated in the requirements for ever smaller devices in the computer chip industry. The electron also carries a magnetic moment which can be represented as the physical observable of a spin quantum number. The research proposed is to search for methods to manipulate the spin phase of the electron waves such as to cause interference. Spin phase can change as the magnetic moment moves through an electric field. Here the internal electric fields existent in compound semiconductors will be exploited. The results of this research will assist in understanding the role of electron spin in quantum dot and ballistic transport experiments implemented in heterojunctions and similar quantum device structures.