Interacting Two-dimensional Electrons in Unconventional Systems

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****Technical Abstract****This study explores electron interaction physics in high-quality, quantum-confined semiconductor structures. The program includes studies of both fabrication, via the molecular beam epitaxy technique, and of electronic transport properties at low temperatures and high magnetic fields where electron correlation phenomena dominate. The emphasis of the work is on novel, high-quality two-dimensional electron systems confined to selectively-doped AlAs and wide GaAs quantum wells. The two-dimensional electrons in AlAs have parameters that are very different from those of the standard two-dimensional electrons in GaAs: they have a much larger and anisotropic effective mass, a much larger effective g-factor, and they occupy multiple conduction band valleys. The electron systems in wide GaAs wells, on the other hand, have thick or bilayer-like charge distributions and can occupy two electric subbands. Both AlAs and wide GaAs two-dimensional electrons thus provide crucial and important test-beds for new many-body physics. Several problems will be studied in the course of this project, including the role of valley, subband, layer, and spin degrees of freedom in determining the electron system's ground states. The project will be carried out by graduate and undergraduate students who will be trained in crucial areas of crystal growth, fabrication, and electrical measurements. ****Non-Technical Abstract****One of the most fascinating areas in solid state physics concerns new states of matter that come about primarily because of the interaction between charged particles such as electrons. To explore such states, one needs specimens in which the imperfections, including impurities and crystal defects, are reduced to a minimum. This study involves the fabrication of such samples, and measurements of their novel electronic properties. The emphasis is on two-dimensional electron systems confined to aluminum-arsenide or gallium-arsenide quantum wells. These materials have parameters that are very different from the commonly studied samples, and provide us with systems that have extra electronic degrees of freedom, such as spin, layer, and valley. An understanding of the states and phenomena observed in the new samples not only will advance our knowledge of fundamental physics, but can also lead to novel device concepts. A major component of this research is the training and education of graduate and undergraduate students in critical areas of crystal growth, semiconductor sample processing, and electrical measurements. Well-trained students in this field will be invaluable resources for the US as well as the rest of the world.