University of Minnesota
School of Physics & Astronomy


As the electron spins

Paul Crowell
Paul Crowell
Alex Schumann

Spintronics is the art of controlling the spin of an electron for use in semiconductors and other materials. The research group of School of Physics and Astronomy Professor Paul Crowell is part of a Minnesota-based collaborative effort that recently solved a long-standing problem in this field.

In Professor Crowell's laboratory the behavior of electron spins in solids is probed on length scales from a few nanometers to many microns and on timescales down to fractions of a nanosecond. Perhaps the most convenient tool for investigating spins in semiconductors is light. Over the last several years, Crowell and his colleagues have used lasers and other tools to detect spins that are injected into semiconductors. This approach works well for fundamental research in a laboratory setting, but in order to integrate spintronics into real-life electronics, physicists have longed for a way to convert electrical signals into spin signals and back again. Working with collaborators from the Department of Chemical Engineering and Materials Science and Los Alamos National Laboratory, Crowell and his students have made a significant step towards this goal. They were able to inject electron spins into a semiconductor, transport the spins over a distance of more than ten microns (about the diameter of a human hair), and were then able to read out the electron spin state electronically.

This result has followed from several years of work by Crowell and his collaborator Chris Palmstrøm on the properties of interfaces between ferromagnetic metals (such as iron) and semiconductors. The most efficient spin transfer between these materials occurs by quantum mechanical tunneling, and the current challenge for the group is to figure out how these tunnel barriers behave at higher temperatures and in the presence of the large currents that may exist in more practical devices.

Crowell’s work is supported by the Office of Naval Research and the National Science Foundation through the University of Minnesota Materials Research Science and Engineering Center

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