Magnetic Material – A New Host to Wily Weyl Fermions

As disclosed by X-ray and neutron research done by a group of scientists lead by the Department of Energy’s Oak Ridge National Laboratory and the University of Tennessee, the existence of the elusive massless particle in a magnetic crystal set up is now possible.

The research group investigated a material containing the dense element osmium and demonstrated two conditions vital for the existence of Weyl fermions – massless particles that were identified in 1929 and witnessed experimentally for the first instance in 2015. Also, researchers are searching for other materials, which could easily host the particles with the aim of harnessing their specific properties in spintronics and innovative computing applications like quantum computers.

As said by ORNL’s Stuart Calder, the very first author of the research team, “Once there are available materials that could hosts these particles, they can act like electrons, but shift at a much faster pace than they are massless. Since the entire electronics is outlined around electrons, so if the electrons are replaced with Weyl fermions then they could support the functioning of much faster devices.”

The team of scientists performed the neutron diffraction studies at the High Flux Isotope Reactor, a DOE Office of Science User Facility at ORNL, for clearly illustrating the magnetic structure of an osmium-based material with a pyrochlore crystalline structure. Their findings reveal that it consist an “all-in, all-out” magnetic mechanism – one of which is one major requirement for such materials to incorporate Weyl fermions.

“It defines the twists of electrons and how they organize, either all of them point out or shift to the center,” says Calder. “Neutrons are the basic and simplest way to identify the magnetic structure. The magnetic current in such materials is fragile as they have smaller size rotations. So if you wish to view them, then you have to use a special instrument.”

The second benchmark is robust spin-orbit coupling, which is a basic property of all atoms that explains how an electron rotates and its movement around an atom are related. In the general case, the bigger atoms with some electrons showcase a powerful spin-orbit effect. But the movement in this material, despite the fact that is a dense and heavy element, has an electron configuration that is considered to reduce the spin-orbit effects.

The researcher’s revealed evidence of powerful spin-orbit linked with the osmate pyrochlore material with use of X-ray tests at the Advanced Photon Source, a DOE Office of Science User Facility at Argonne National Laboratory.

“It is predictable that the spin-orbit joint effect in osmium must be suppressed or ignored in this pyrochlore material, but it was for the first instance that anyone measured osmium-based source with the use of X-ray technique. The concern of the X-ray was to highlight traits of robust spin-orbit coupling and that is what is identified, “says Calder.

Calder attentiveness is towards the fact that the research work done by the team is not a direct confirmation of Weyl fermions in an osmate material, but it truly advocates that such a material is a budding host.