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.

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.


You might also be interested in

  • Unconventional piezoelectricity in ferroelectric hafnia
    Science Highlight
    Unconventional piezoelectricity in ferroelectric hafnia
    Hafnium oxide thin films are a fascinating class of materials with robust ferroelectric properties in the nanometre range. While the ferroelectric behaviour is extensively studied, results on piezoelectric effects have so far remained mysterious. A new study now shows that the piezoelectricity in ferroelectric Hf0.5Zr0.5O2 thin films can be dynamically changed by electric field cycling. Another ground-breaking result is a possible occurrence of an intrinsic non-piezoelectric ferroelectric compound. These unconventional features in hafnia offer new options for use in microelectronics and information technology.
  • Sodium-ion batteries: How doping works
    Science Highlight
    Sodium-ion batteries: How doping works
    Sodium-ion batteries still have a number of weaknesses that could be remedied by optimising the battery materials. One possibility is to dope the cathode material with foreign elements. A team from HZB and Humboldt-Universität zu Berlin has now investigated the effects of doping with Scandium and Magnesium. The scientists collected data at the X-ray sources BESSY II, PETRA III, and SOLARIS to get a complete picture and uncovered two competing mechanisms that determine the stability of the cathodes.
  • BESSY II: Molecular orbitals determine stability
    Science Highlight
    BESSY II: Molecular orbitals determine stability
    Carboxylic acid dianions (fumarate, maleate and succinate) play a role in coordination chemistry and to some extent also in the biochemistry of body cells. An HZB team at BESSY II has now analysed their electronic structures using RIXS in combination with DFT simulations. The results provide information not only on electronic structures but also on the relative stability of these molecules which can influence an industry's choice of carboxylate dianions, optimizing both the stability and geometry of coordination polymers.