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.
- Key technology for a future without fossil fuelsIn June and July 2025, catalyst researcher Nico Fischer spent some time at HZB. It was his sabbatical, he was relieved of his duties as Director of the Catalysis Institute in Cape Town for several months and was able to focus on research only. His institute is collaborating with HZB on two projects that aim to develop environmentally friendly alternatives using innovative catalyst technologies. The questions were asked by Antonia Rötger, HZB.
- Scrolls from Buddhist shrine virtually unrolled at BESSY IIThe Mongolian collection of the Ethnological Museum of the National Museums in Berlin contains a unique Gungervaa shrine. Among the objects found inside were three tiny scrolls, wrapped in silk. Using 3D X-ray tomography, a team at HZB was able to create a digital copy of one of the scrolls. With a mathematical method the scroll could be virtually unrolled to reveal the scripture on the strip. This method is also used in battery research.
- Helmholtz Doctoral Award for Hanna TrzesniowskiDuring her doctoral studies at the Helmholtz Centre Berlin, Hanna Trzesniowski conducted research on nickel-based electrocatalysts for water splitting. Her work contributes to a deeper understanding of alkaline water electrolysis and paves the way for the development of more efficient and stable catalysts. On 8 July 2025, she received the Helmholtz Doctoral Prize, which honours the best and most original doctoral theses in the Helmholtz Association.