Science often surprises us. An idea that seems only of academic concern sparks a thought that cascades into new directions, and every so often, one of them leads to a transforming technology. Without the first basic-science step, such a process would be impossible. The spin Hall effect (SHE) is a fascinating example of that scientific multibranching process that also demonstrates how fundamental research is essential for future technology.

The effect is relatively easy to describe. When current flows in a nonmagnetic solid, the moving electrons can feel a spin-dependent deflecting force perpendicular to their velocity. That force drives spin-up electrons predominantly to one side and spin-down electrons predominantly to the other. The result, as illustrated in figure 1a, is a spin current perpendicular to the charge current.

Russian physicists Mikhail Dyakonov and Vladimir Perel first proposed1 the SHE in 1971. They combined ideas from two sources. One was...

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