Electron and Nuclear Spin Interactions in Low-Dimensional Semiconductors

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Non-Technical Electrons are fundamental particles that have spin, mass, and charge. The understanding of electronic energy levels has been crucial to understanding chemistry and the development of solid-state materials, such as semiconductors, which have enabled technologies such as computer chips, light-emitting diodes, and solar cells. The logic elements in today's computer chips rely on controlling electron charge and encode information as the presence or absence of charge currents and voltages, but encoding information using electron spin polarization has applications for quantum information processing and potential advantages for improving the speed, efficiency, and energy consumption of logic devices. Electron spins, however, also interact with nuclear spins, and this can be an undesirable source of noise or, if we can understand it better, a pathway for controlling electron spin polarization. The PI will use optical measurements with pulsed lasers to characterize how these spin interactions depend on material strain and other parameters. This research will improve the scientific understanding of these interactions and help us figure out how to control them. The results of this research have the potential to advance multiple scientific and technological areas, including semiconductor physics, device engineering, materials science, magnetism and quantum information. The research will provide valuable training to student researchers in a wide range of techniques, including semiconductor device design and fabrication, optical and electrical measurements, data acquisition and analysis and communicating results through scientific presentations and publications. The proposed outreach and education activities will seek to increase public engagement with recent developments in science and technology and to encourage the participation of underrepresented groups in scientific careers. Technical The proposed research will investigate electron and nuclear spin interactions in low-dimensional semiconductor heterostructures. Controlling the interactions between electron and nuclear spins is of great importance for applications such as classical and quantum information processing, but the understanding of the coupled electron-nuclear spin system is incomplete. Recent experiments on strained quantum dots have revealed unexpected phenomena, including nuclear spin locking, nuclear magnetization at zero magnetic field, and the anomalous Hanle effect. These phenomena have been variously attributed to the effects of quantum confinement, mesoscopic size, and strain, but it is difficult to separate these effects in quantum dots and establish the underlying physical mechanisms. The proposed measurements on strained and unstrained quantum wells will elucidate the role of quantum confinement, carrier localization, reduced symmetry and dimensionality, and spin-orbit effects on electron-nuclear spin interactions. The nuclear polarization will be monitored using ultrafast pump-probe and spin noise optical techniques capable of sensitively measuring small changes to the nuclear spin polarization. The proposed research will advance scientific understanding of the physical origins of recently-observed phenomena in strained quantum dots and address open questions about the coupled electron-nuclear spin system and its interaction with light.