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Surprising Control over Photoelectrons from a Topological Insulator Print
Tuesday, 12 March 2013 00:00

Topological insulators are insulators in the bulk but metals on the surface, and the electrons that flow swiftly across their surfaces are “spin polarized.” Surface-electron spin and momentum are locked, offering new ways to control electron flow and distribution in spintronic devices. A Nature Physics paper by first author Chris Jozwiak of the Advanced Light Source and a large team led by Alessandra Lanzara and Zahid Hussain describes surprising results counter to previous assumptions: the spin polarization of photoemitted electrons from the surface of a topological insulator is wholly determined in three dimensions by the polarization of the incident light beam.

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The diagram at right shows the electronic states of bismuth selenide in momentum space. ARPES, at left, can directly create such maps with photoelectrons. A slice through the conduction cone at the Fermi energy maps the topological insulator’s surface as a circle (upper left); here electron spins and momenta are locked together. Initial ARPES measurements in this experiment were made with p-polarized incident light in the regions indicated by the green circle and line, where the spin polarization of the photoelectrons is consistent with the intrinsic spin polarization of the surface.