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Evidence for Weyl fermions The key to a new generation of high-speed, low-power information technologies

January 25, 2021

For the first time, researchers provide concrete evidence for a rare physical property known as a Weyl semimetal state by creating two special materials known as antiferromagnets. Weyl semimetal states give rise to certain electronic and magnetic effects that could help realize a generational leap in the speed and efficiency of computational electronic devices.

The continuing race to improve technology triggers great interest in searching for new materials with exotic properties. Antiferromagnets possessing so-called topological states are considered one such type of material ideal for next-generation spintronic applications that could outperform today’s electronic-based devices. The reason for this is their ability to perform ultrafast switching operations, the basis of digital computation, in the region of a thousand times faster than current computer processors. Antiferromagnets are also stable against stray magnetic fields that might otherwise disrupt a present-day device.

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Weyl Fermion. A microscopic section of the manganese and tin crystal made visible by a process called angle-resolved photoemission spectroscopy. © 2021 Springer Nature

“The two antiferromagnetic materials we investigated are based on manganese and either tin or germanium. We created high-quality single crystals of these materials which are essential to detect the physical signatures we were looking for,” said Project Researcher Susumu Minami of the Department of Physics. “Previous research has shown that the materials exhibit the effects that will make them useful in devices one day, the anomalous Hall effect (AHE) and anomalous Nernst effect (ANE). We sought the underlying property that gives rise to these and we have now discovered it in the form of a property called a Weyl semimetal state or Weyl fermion.”

Crucially, AHE and ANE were seen to occur at room temperature in manganese-based crystals. Often, advances in functional materials that exploit microscopic quantum phenomena require ultracold temperatures. A famous example of this would be quantum computers which are chilled to several hundred degrees below the freezing point of water. However, AHE and ANE are examples of spintronic phenomena that offer potential advancements in the power of functional devices and could even improve the efficiency of energy harvesting technology at room temperature.

“Our discovery signifies an experimental breakthrough in this direction, but there is still much work to do,” said Minami. “Direct detection of the Weyl fermion is extremely challenging. For one thing, we will need to synthesize even larger crystals to acquire more accurate measurements. Only then can we form general theories on how to create larger AHE and ANE, which will allow practical devices to be engineered. This is a long and challenging journey, but it is rewarding to make it happen.”

Papers

Taishi Chen, Takahiro Tomita, Susumu Minami, Mingxuan Fu, Takashi Koretsune, Motoharu Kitatani, Ikhlas Muhammad, Daisuke Nishio-Hamane, Rieko Ishii, Fumiyuki Ishii, Ryotaro Arita & Satoru Nakatsuji, "Anomalous transport due to Weyl fermions in the chiral antiferromagnets Mn3X, X = Sn, Ge," Nature Communications: January 25, 2021, doi:10.1038/s41467-020-20838-1.
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