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.
- Only at BESSY II worldwide: IR nanoscopy at very long THz wavelengthsThe team at the IRIS beamline at BESSY II has created a new experimental option: They achieved infrared nanoscopy with a spatial resolution of around 50 nm at very long THz wavelengths. This was possible thanks to a temporal pattern of light pulses known as the low-alpha operating mode at BESSY II. Worldwide, BESSY II is the only synchrotron light source at which users could perform nanoscopy in a single setup from 25 to 4000 cm-1, a unique opportunity for ultra-broadband characterisation of complex materials at the nanoscale in both the life sciences and materials sciences.
- Ultrafast demagnetisation - Thinner iron, stronger effectThe thinner an iron film, the more easily it can be demagnetised by a laser pulse. Researchers at the University of Duisburg-Essen, working with Helmholtz-Zentrum Berlin and other partners, have discovered why: the key lies in the magnetic order at the material's interfaces. In the long term, these findings could contribute to the development of new technologies for magnetic data storage. The results have been published in the scientific journal Advanced Science.
- Blind spot for the arrangement of atomsArtificial intelligence is increasingly being used to predict the properties of new materials. A research team from Jena and the United States now shows in a study published in the journal Nature Computational Science that when language models are used for this purpose, they reliably identify which types of atoms a material contains. However, they make insufficient use of information about how those atoms are arranged in space. Neither larger models nor additional training data resolve this weakness. For material properties that depend strongly on structure, AI models specifically designed to process spatial relationships are therefore the more reliable choice. (DOI: 10.1038/s43588-026-01045-2)