This project will advance the understanding of charge and spin transport in semiconductors under conditions that are very far from equilibrium. The research addresses new devices in which spin currents in semiconductors are generated and detected using ferromagnetic metals. The experiments will address how fundamental phenomena such as the spin-orbit interaction, hyperfine interactions, hot electron populations, and dimensionality impact spin-polarized transport. First, a set of experiments will be carried out to elucidate the connection between the spin Hall effect in semiconductors, which has only recently been observed in transport measurements, and its inverse effect, in which a spin-polarized current generates a charge current. A second set of experiments will probe spin-polarized carriers far from equilibrium, where departures from ordinary linear response have recently been observed. The potential for using these non-linear effects to control spin currents will be demonstrated. Third, the manifestation of spin-orbit coupling in traditional transport effects, including weak-anti-localization, will be correlated with direct measurements of the spin transport and dynamics using techniques developed in the PI's group. Finally, the proposed research will address some of the critical steps required to undertake similar experiments in reduced dimensions. These experiments address some of the critical steps required to implement devices, such as a spin transistor, which will require a deeper understanding of ferromagnet-semiconductor heterostructures.

Nontechnical Abstract

Magnetism is ubiquitous in modern technology. Mass data storage, as in computer hard drives, depends on the magnetism of metals, such as iron, cobalt or nickel. Semiconductors, while also a critical component of modern technologies, are not magnetic. This project focuses on a materials system that is made out of thin layers of a ferromagnetic material (iron) and a semiconductor. The ultimate goal of this line of research is the achievement of new classes of devices that carry out both the processing and storage of information on a single chip. This project focuses on fundamental properties that determine how electron spins (the carriers of magnetic information) can be injected, controlled, and detected inside a semiconductor. The research will include experiments probing the new and unusual conditions present when spins in semiconductors are generated near surfaces, in very large numbers, or in very thin layers. These physical phenomena lie at the heart of new proposals for magneto-electronic devices that could be enabled by this research.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Guebre X. Tessema
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University of Minnesota Twin Cities
United States
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