How to use light to manipulate the spin in topological insulators
The picture shows the characteristic spin texture (arrows) in a topological insulator and how it is manipulated by circularly polarized light. © Rader/Sachez-Barriga/HZB
Researchers at 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.
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.
- Superconducting TES array X-ray spectrometer goes into operation at BESSY IIThe TES-Spectrometer was developed within a collaboration between the HZB, the MPI-CEC (Mühlheim-an-der-Ruhr, Germany) and the NIST (Boulder CO, USA) and is now in operation at BESSY II, as the only TES-Spectrometer at a synchrotron source in Europe. The photon detection efficiency of the new instrument exceeds that of wavelength-dispersive X-ray emission spectrometers by a factor of 100 to 1000. It will be used to investigate the electronic properties of atomically thin layers, nanostructures and highly diluted atomic and molecular samples. The team is looking forward to receiving exciting research proposals from the user community.
- Magnon momentum microscopy: A new window into nanoscale spin-wavesAn international team lead by the Max Born Institute has developed a new type of momentum microscopy to image magnons — the quanta of collectively excited spins — directly in two-dimensional reciprocal space using soft X-rays. Measurements have taken place at BESSY II and PETRA III, first author ist the HZB physicist Steffen Wittrock. Owing to its remarkable sensitivity, simplicity, and access to nanometer-scale wavelengths, this novel technique establishes a powerful and versatile platform for exploring nonlinear magnon interactions, which are promising for future computing schemes.
- BESSY II: How intrinsic oxygen shortens the lifespan of solid-state batteriesAlthough solid-state batteries (SSBs) demonstrate high performance and are intrinsically safe, their capacity currently declines rapidly. A team from the TU Wien, Humboldt-University Berlin and HZB has now analysed a TiS₂|Li₃YCl₆ solid-state half-cell in operando at BESSY II using a special sample environment that allows for non-destructive investigation under real operating conditions. Data obtained by combination of soft and hard X-ray photoelectron spectroscopy (XPS and HAXPES) revealed a new degradation mechanism that had not previously been identified in solid-state batteries. They have gained some surprising insights, particularly regarding the harmful role played by intrinsic oxygen. This study provides valuable information for improving design and handling of such batteries.