Applying an electric field along a frigid strip of near-defect-free semiconductor can drive a lateral imbalance of spin-up and spin-down electrons, a spin Hall effect. The effect, which comes in several varieties, depends at heart on the coupling between the electrons’ spin and orbital angular momentum (see Physics Today, Physics Today 0031-9228 58 2 2005 17 https://doi.org/10.1063/1.2169428 February 2005, page 17 and Physics Today 0031-9228 61 1 2008 19 https://doi.org/10.1063/1.2835139 January 2008, page 19 ).
Light can have both spin—in the form of circular polarization—and orbital angular momentum or helixity. Could coupling between the two momenta engender a spin Hall effect for light? As Onur Hosten of the University of Illinois at Urbana-Champaign and his thesis adviser Paul Kwiat demonstrate in a new experiment, the answer is yes. 1
In the Illinois experiment, the role of the electric field was played by a step-wise gradient in refractive index. The...
