Scientific Highlights

Flows need sources and sinks. That’s why, in a new class of exotic materials called Weyl semimetals, the sources and sinks of Berry curvature – dubbed Weyl points – were believed to exist only in pairs. Now researchers at PSI have observed unpaired Weyl points for the first time in a crystalline solid. This discovery, which upends conventional thinking and the so-called Nielson-Niomiya no-go theorem, demonstrates the unique properties of "nodal wall" Weyl semimetals in comparison to conventional Weyl systems having only zero-dimensional Weyl nodes.

Within this synergetic collaboration, PSI scientists have investigated the correlation between magnetic and electronic ordering in NdNiO3 by tuning its properties through proximity to a ferromagnetic manganite layer. The main outcome is that the stray magnetic field from the manganite layer causes a novel ferromagnetic-metallic (FM-M) phase in NNO. This work demonstrates the utilization of heterostructure engineering for creating novel quantum phases.

Researchers from University of Zurich describe the experimental observation of a new orthorhombic structural phase in the superconducting iron-pnictide compound Pr₄Fe₂As₂Te_0.88O₄. In contrast to nematicity found in underdoped iron pnictides this phase transition is not electronically driven. 

Researchers at NCCR MARVEL have combined first principles calculations with soft X-ray angle-resolved photoemission spectroscopy to examine tungsten diphosphide’s electronic structure, characterizing its Weyl nodes for the very first time. In agreement with density functional theory calculations, the results revealed two pairs of Weyl nodes lying at different binding energies. The observation of the Weyl nodes, as well as the tilted cone-like dispersions in the vicinity of the nodal points, provides compelling evidence that the material is a robust type-II Weyl semimetal with broken Lorentz invariance. This is as MARVEL researchers predicted two years ago. The research has been published in Physical Review Letters as an Editor's Suggestion.