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Weyl fermions were discovered in another class of material

  Weyl fermions were discovered in another material class
The 3 PSI researchers Junzhang Ma, Ming Shi and Jasmin Jandke (left to right) at the Swiss Light Source SLS, where they managed to prove the presence of Weyl fermions in paramagnetic material . Credit: Paul Scherrer Institute / Markus Fischer

A special type of elemental particle, the Weyl fermions, was first discovered a few years ago. Their specialty: they move through a material in a well-defined manner that almost never lets them collide with each other and are thus very energy efficient. This gives rise to exciting opportunities for future electronics. So far, Weyl fermions have only existed in certain non-magnetic materials. For the first time, researchers at Paul Scherrer Institute PSI have experimentally proven their existence in another type of material: a paramagnet with inherent slow magnetic fluctuations. This result also shows that it is possible to manipulate the Weyl fermions with small magnetic fields, which possibly enables use in spintronics, a promising development in electronics for new computer technology. The researchers published their findings in the scientific journal Science Advances .

Among the approaches that could pave the way to future energy-efficient electronics, Weyl fermions could play an exciting role. Found experimentally only in materials such as quasi-particles, they behave like particles that have no mass. Assuming theoretically in 1

929 by mathematician Hermann Weyl, their experimental discovery of researchers at PSI came first in 2015. So far, Weyl fermions have only been observed in some non-magnetic materials. But a team of researchers at PSI along with researchers in the US, China, Germany and Austria also found them in a specific paramagnetic material. This discovery can lead to a potential use of Weyl fermions in future computer technology one step closer.

Searching for Slow Magnetic Fluctuations

"The Difficult Part," says Junzhang Ma, postdoctoral researcher at PSI and first author of the new study, "was to identify a suitable magnetic material to look for these Weyl fermions." For years, although the accepted theoretical assumption had been to exist in certain magnetic materials Weyl fermions, experimental evidence of this still sought great effort from several research groups worldwide. The team of researchers at PSI then had an idea to focus their attention on a particular group of magnetic materials: paramagnets with slow magnetic fluctuations.

"In specific paramagnetic materials, these inherent magnetic fluctuations could be sufficient to create a pair of Weyl fermions," said Ming Shi, professor of the same research group as Ma: Spectroscopy of Novel Materials Group. "But we understood that the fluctuations must be slow to show the Weyl fermions. From this time on, identification of which material had sufficiently slow magnetic fluctuations could become our primary challenge. "

Since the characteristic time of magnetic fluctuations is not a function that can be controlled in a reference work for each material, the researchers did little. time and effort to find a suitable material for their experiments, model analysis in theoretical physics made on PSI helped them identify a promising candidate with slow magnetic fluctuations: the material with the chemical notation EuCd 2 As 2 : Europium-Cadmium-Arsenic, and in this paramagnetic material, the researchers could experimentally prove Weyl fermions

Measurements with Muons and X-ray

The researchers used two of PSI's major research facilities for their experiments: First, the employee the Swiss Muon Source (SμS) for measuring and better characterization magnetic fluctuations in their material. Then, the Weyl fermions were visualized with an X-ray spectroscopy method at Swiss Light Source SLS.

"What we have proven here is that Weyl fermions can exist in a wider range of materials than previously thought," says Junzhang Ma. The researchers' research thus substantially spans the range of materials that are considered viable in the search for materials that are suitable for the electronics of the future. In a development area called spintronics, Weyl fermions can be used to transport information with much higher efficiency than that achieved by electrons in today's technology.

Chiral zero sound found in Weyl semimetals

More information:
"Spin Fluctuation Induced Weyl Semimetal State in the Paramagnetic Phase of EuCd Science Advances (2019). DOI: 10.1126 / sciadv.aaw4718, https://advances.sciencemag.org/content/5/7/eaaw4718

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Paul Scherrer Institute

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Weyl fermions discovered in another class of material (2019, July 12)
July 12, 2019
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