****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 electrons. To explore such states, one needs specimens in which the imperfections, including impurities and crystal defects, are reduced to a minimum. This individual investigator award supports a project involving the fabrication of such samples, and measurements of their novel electronic properties. The emphasis is on two-dimensional electron systems in aluminum-arsenide quantum wells. These have parameters that are very different from the commonly studied gallium-arsenide samples. 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.
This individual investigator award supports a project to explore and elucidate electron interaction physics in high-quality, quantum-confined semiconductor structures. The program includes studies of 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 (2DESs) confined to selectively-doped AlAs quantum wells; these 2DESs have parameters that are very different from those of the standard 2DESs in GaAs. Several problems, including the influence of the spin and valley degrees of freedom on the integer and fractional quantum Hall states will be investigated. Graduate and undergraduate students will be involved with these experimental research projects. The students will be trained in crucial areas of crystal growth, fabrication, and electrical measurements.
This project dealt with an experimental investigation of electron interaction physics in high-quality, quantum-confined semiconductor structures. The program included 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 was on high-quality two-dimensional electron systems confined to selectively-doped aluminum-arsenide quantum wells. The two-dimensional electrons in aluminum-arsenide have parameters that are very different from those of the standard two-dimensional electrons in gallium-arsenide: they have a much larger and anisotropic effective mass, a much larger effective Lande g-factor, and they occupy multiple conduction band valleys. Since these parameters influence the electron-electron interaction, aluminum-arsenide two-dimensional electrons provide a crucial and important test-bed for new many-body physics. Several problems were studied in the course of this project, including the role of valley and spin degrees of freedom and the anisotropic effective mass on the ground states of the system in general, and on the integer and fractional quantum Hall states in particular. The results of the research were 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 will benefit society in the long term as it may lead to novel, transformative concepts for electronic devices and information processing systems whose operation relies on quantum and/or interaction phenomena. The project also incorporated a high quality and comprehensive educational component, resulting in the education of students in critical, state-of-the art areas of science and technology, including the fabrication, characterization, and physics of high quality layered semiconductor structures. Well-trained students in these fields will be invaluable resources for the US as well as for the rest of the world.
