Fermi Arcs in an Antiferromagnet detected at BESSY II
The Fermi surface of antiferromagnetic NdBi taken at 6 K temperature at BESSY II. It shows so called Fermi arcs. © https://www.nature.com/articles/s41586-022-04412-x.
An international cooperation has analysed samples of NdBi crystals which display interesting magnetic properties. In their experiments including measurements at BESSY II they could find evidence for so called Fermi arcs in the antiferromagnetic state of the sample at low temperatures. This observation is not yet explained by existing theoretical ideas and opens up exciting possibilities to make use of these kind of materials for innovative information technologies based on the electron spin rather than the charge.
Neodymium-Bismuth crystals belong to the wide range of materials with interesting magnetic properties. The Fermi surface which is measured in the experiments contains information on the transport properties of charge carriers in the crystal. While usually the Fermi surface consists of closed contours, disconnected sections known as Fermi arcs are very rare and can be signatures of unusual electronic states.
Unusual magnetic splittings
In a study, published now in Nature, the team presents experimental evidence for such Fermi arcs. They observed an unusual magnetic splitting in the antiferromagnetic state of the samples below a temperature of 24 Kelvin (the Néel-temperature). This splitting creates bands of opposing curvature, which changes with temperature together with the antiferromagnetic order.
These findings are very important because they are fundamentally different from previously theoretically considered and experimentally reported cases of magnetic splittings. In the case of well-known Zeeman and Rashba splittings, the curvature of the bands is always preserved. Since both splittings are important for spintronics, these new findings could lead to novel applications, especially as the focus of spintronics research is currently moving from traditional ferromagnetic to antiferromagnetic materials.
- Science in Berlin: collaborative, diverse, innovative, internationalScience is a key social and economic factor for Berlin. It creates jobs and adds value, attracts talent from all over the world, and enriches city life. To ensure that Berlin remains one of the world’s leading centres of science in the future, science must feature even more prominently on the political agenda. This is what BR50 stands for: over 50 non-university research institutions, including the HZB, are joining forces in this network. Following the election in Berlin, BR50 is now addressing politicians with a position paper, accompanied by the campaign “𝗪𝗶𝗿 𝗳𝗼𝗿𝘀𝗰𝗵𝗲𝗻 𝗳ü𝗿 𝗕𝗲𝗿𝗹𝗶𝗻.”
- Does African Architecture exist?The world’s first Pan-African Architecture Biennale took place this September in Nairobi, Kenya. People from the worlds of architecture, art, academia and politics from 54 African countries and the diaspora had travelled to Nairobi to exchange ideas on traditional and contemporary building methods, materials, experiences and projects. Samira Aden co-organised this biennial as lead curator. We spoke to her about it.
- Nanosilver as an electrocatalyst for CO₂ reductionVia electrolysis, CO2 can be reduced to CO, a raw material for further chemical products such as fuels. Within the GreenQuest Project, an internation team led by HZB chemist Prashanth Menezes has now systematically investigated catalyst layers made of silver nanoparticles, varying both the size of the particles and their density. The best yield was achieved with nanoparticles with diameters of around 10 nm, which were loosely distributed. Furthermore, they demonstrated how the economic efficiency of the electrochemical cell can be enhanced by integrating an additional chemical reaction at the anode, enabling the simultaneous production of a valuable formic acid, hydrogen, and CO in one device.