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Posted: Feb 25, 2014

How to use light to manipulate the spin in topological insulators

(Nanowerk News) Researchers at Helmholtz Zentrum Berlin (HZB) investigated the topological insulator bismuth selenide (Bi2Se3) by spin-resolved photoelectron spectroscopy at BESSY II. They found an astonishing difference depending on whether it is illuminated by circularly polarized light in the vacuum ultraviolet (50 electron volts, eV) and in the ultraviolet spectral range (6 eV). This result could help explaining how spin currents can be generated in topological insulators.
In the former case, the emitted electrons display the characteristic spin texture of topological insulators, which is aligned on a circle in the surface plane, similarly to a roundabout road sign. In the latter case, however, the spins do not only rotate completely out of this plane but also take on the spin direction imposed by the right or left circularly polarized light.
characteristic spin texture (arrows) in a topological insulator
The picture shows the characteristic spin texture (arrows) in a topological insulator and how it is manipulated by circularly polarized light.(Image: Rader/Sachez-Barriga/HZB)
HZB researchers expect that this manipulation of the electron spin by light and the insight into its preconditions will be most useful for the generation of lossless spin currents in topological insulators.
Topological insulators are a novel state of matter with an insulating bulk and a metallic surface, which are interesting candidates for novel devices in future information technologies. Light-induced spin manipulation is one of the processes involved.The present work reveals the conditions for the generation of dissipationless spin currents in topological insulators.
Their results have just been accepted for publication in Physical Review X, the new top journal of the Americal Physical Society ("Photoemission of Bi2Se3 with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?").
Source: Helmholtz Zentrum Berlin
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