Probing Exotic Phases of Two-dimensional Electrons in Unconventional Systems

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Nontechnical Abstract:One of the major research areas in solid-state science and engineering involves the study of how the electrons in a solid interact. The interaction often leads to exotic, often unexpected, phases of matter. To study these phases and phenomena, it is important to minimize the imperfections, such as impurities and defects. The goal is to experimentally explore and understand the new phases that arise in electron systems with the least amount of imperfections. Results of the research are communicated through publications and conference presentations to the specialized as well as general science and engineering communities. While the subject of this work is fundamental, progress in this area benefits society in the long term as it may lead to novel, transformative concepts for electronic devices and information processing systems, such as a quantum computer, whose operation relies on quantum and/or interaction phenomena. The project also incorporates a high quality and comprehensive educational component as it includes the education of students in critical, state-of-the art areas of science and technology, including the fabrication, characterization, and physics of very high-quality, thin-film semiconductor structures. Well-trained students in these fields are invaluable resources for the US as well as for the rest of the world. Technical Abstract:This project encompasses an experimental investigation of electron interaction physics in high-quality, quantum-confined semiconductor structures. The research includes studies of both fabrication, via the molecular beam epitaxy technique, and of the electronic transport properties at low temperatures and high magnetic fields where electron correlation phenomena dominate. The emphasis of the work is on high-quality two-dimensional electron systems confined to selectively-doped AlAs and bilayer 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 Lande g-factor, and they occupy multiple conduction band valleys. The bilayer electron systems in GaAs double quantum wells, on the other hand, are specifically designed so that the measured electronic properties of one layer could be used to probe the physics of the other layer. An example is a system where the composite fermions in a layer with high density are used to probe a Wigner crystal formed in an adjacent low-density layer. Both AlAs and bilayer GaAs two-dimensional electrons thus provide crucial and important test-beds for new many-body physics. Several exotic phases of interacting two-dimensional electron systems are studied during the course of this project; these include the fractional quantum Hall effect, composite fermions, Wigner crystal, and stripe phases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.