BESSY II: Experimental verification of an exotic quantum phase in Au2Pb
The figure shows the measured energy-momentum relationship for Au2Pb. The linear behavior is evidence for a Dirac semimetal. In addition, a Lifshitz transition is observed: At temperatures 223 K and below, the electrons behave like positively charged particles, whereas at room temperature they behave like negatively charged ones. © HZB
A team of HZB has investigated the electronic structure of Au2Pb at BESSY II by angle-resolved photoemission spectroscopy across a wide temperature range: The results are in accordance with the electronic structure of a three-dimensional topological Dirac semimetal, in agreement with theoretical calculations.
The experimental data unveil some very special features linked to a Lifshitz transition. The study broadens the range of currently known materials exhibiting three-dimensional Dirac phases, and the observed Lifshitz transition demonstrates a viable mechanism to switch the charge carrier type in electric transport without the need for external doping. Moreover, the material becomes interesting as candidate for the realization of a topological superconductor.
The study which includes theory from San Sebastian and synthesis from Princeton was highlighted as Editor's Suggestion in the journal Physical Review Letters.
- New contact material boosts the efficiency of perovskite solar cellsA newly developed material for the electron contact improves the efficiency of single perovskite solar cells and perovskite/silicon tandem solar cells. The new material is based on a carborane molecule. It offers several advantages over the standard material C60, as shown by the study led by Steve Albrecht’s team. The new material has since been patented and is already commercially available.
- BESSY II: New sample environment allows glimpse into thermocatalytic processesA novel measurement cell allows, for the first time, soft and hard X-ray investigations under high pressures of up to 20 bar and temperatures of up to 400°C. This provides new insights into thermocatalytic processes, such as the Fischer-Tropsch synthesis for producing synthetic fuels. The development of the measurement cell is considered a significant achievement within the Care-O-Sene project.
- Precision interface chemistry pushes perovskite solar cells beyond 26% efficiencyAn international research collaboration has developed a new molecular strategy for controlling one of the most critical interfaces in perovskite solar cells. The resulting solar cells reached a power conversion efficiency of 26.19% in the n i p architecture, together with strong operational stability under prolonged illumination and elevated temperature. The results have been published in the Journal of the American Chemical Society.