Probing Exotic Phases of Ultra High Mobility Two-Dimensional Electrons

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Non-technical Description:A major research area in solid-state science and engineering is the study of how the electrons in a solid interact. The interaction stems from the repulsion between electrons because of their electric charge, as well as their spin and other degrees of freedom. It 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, so that electron-electron interaction is the dominating factor. The goal of this project 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 project 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 Description:This project encompasses experimental investigations of electron interaction physics in quantum-confined GaAs/AlGaAs semiconductor structures with ultra-high-quality, as quantified by their record-high mobilities and new many-body states. The program 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 two-dimensional electron and hole systems confined to selectively doped GaAs quantum wells. The two-dimensional electron systems have the highest mobility among all solid-state materials, while the larger effective mass and the strong spin-orbit interaction in two-dimensional hole systems add additional, novel twists to their electronic properties. Several exotic phases of these interacting two-dimensional carrier systems are studied during the course of this project; these include the fractional quantum Hall effect, composite fermions, Wigner crystal, and stripe and bubble phases. Competition between the fractional quantum liquid and the Wigner crystal at large perpendicular magnetic fields (small Landau level filling factors), as well as many-body states in excited Landau levels are being investigated.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.