1. Physics Department, University of California, Berkeley, and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
2. Laboratory for Molecular Sciences, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
3. Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA

Correspondence to: C. P. Weber¹ Correspondence and requests for materials should be addressed to C.P.W. (Email: cpweber@lbl.gov).

Abstract

An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin that offer potential advantages in dissipation, size and speed over charge-based devices¹. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (- e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves². In contrast, the electron's spin along a given spatial direction can take on two values, /2 (conventionally ,), so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron–electron (e–e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but also that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e–e collisions.

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