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Silicon based device is sensitive to photon spin, say scientists

A research team from the University of Pennsylvania has demonstrated a silicon based photonic device that is sensitive to the spin of the photons in a laser shined on one of its electrodes. According to the team, light that is polarised clockwise causes current to flow in one direction, while anticlockwise polarised light makes it flow in the other direction.

The property is said to be a function of the geometric relationship between the pattern of atoms on the surface of silicon nanowires and how electrodes placed on those wires intersect them. The interaction between the semiconducting silicon and the metallic electrodes produces an electric field at an angle that breaks the mirror symmetry that silicon typically exhibits, sending electrons in one direction or the other down the nanowire.

Professor Ritesh Agarwal said: "Whenever you change a symmetry, you can do new things. In this case, we have demonstrated how to make a photodetector sensitive to a photon's spin. All photonic computers need photodetectors, but they currently only use the quantity of photons to encode information. This sensitivity to photon spin would be an extra degree of freedom, meaning you could encode additional information on each photon.

"Typically, materials with heavy elements show this property due to their spins strongly interacting with electron's orbital motion. But we have demonstrated this effect on the surface of silicon, originating only from the electron's orbital motion."

Prof Agarwal's team is now working on ways to get planar silicon to exhibit these properties using the same mechanism.

Graham Pitcher

Source:  www.newelectronics.co.uk

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