New spin on the Hall effect

摘要

The spin Hall effect occurs when electrons with opposite spins go their separate ways in an electric field. The phenomenon is crucial to spin-based electronics, and its electrical signal has just been spotted. Just as manipulating election charge is central to conventional electronic circuitry, so creating, moving and measuring electron spin is essential to spin-based electronics, or spin-tionics. On page 176 of this issue, Valenzuela and Tinkham report a breakthrough in spin control, with the firstdetection by electrical means of the 'spin Hall effect' - the separation, or polarization, of electrons of opposite spin (up and down) under the influence of an electric field. Normally, electron spins are polarized by magnetic fields Electrons in so-called ferromagnetic materials (iron is the classic example) are naturally spin-polarized; generating currents of spin in non-magnetic materials has therefore typically involved careful engineering of ferromagnetic contacts that can act as a source of polarized electrons. Alternatively, in semiconductors, polarized laser light has been used to create spin polarization.