Weyl fermions, massless quasiparticles that were predicted to exist in 1930 by mathematician H. Weyl, were first detected separately by three independent research groups in 2015.
Soon after that experimental detection, WVU theoretical physicist Aldo Romero, an associate professor of condensed matter theory and computation, and physics PhD student Sobhit Singh, proposed a way to gain control over the dynamics of these quasiparticles: by creating them in pairs. Their theory, published in Physical Review, was confirmed in an independently performed experiment published in Science earlier this year.
“I think not only us but all the agencies in the U.S. have recognized that this research has a very bright future,” Romero said. “The idea is not only being able to find novel materials but developing devices to use those properties.”
By creating these quasiparticles in pairs, they can be moved and manipulated in a controlled manner. Singh compares the coupling to a dance.
“This is something like a dance, where each couple performs according to the beats, rhythm of the music and the steps of that specific dance style,” Singh said. “In crystals, the interaction between the spin and orbital motions of electrons, or the spin-orbit coupling, plays the beat. An external electric field acts as music, and the crystal symmetries govern the possible motion of electrons. A pair of Weyl fermions forms the dancing couple.”
The quasiparticles are exotic in nature because this spin gives them another degree of freedom in addition to electricity, making them more sensitive to many properties and allowing them to be manipulated in different ways.
“Because of this additional degree of freedom, we can couple the quasiparticles to other degrees of freedom. For example, we can apply light and see the response of it based on the spin. We can apply temperature and see what the changes will be with respect to the spin. We can apply a magnet and see the response with respect to the spin and things like that,” Romero said. “Because we have this new degree of freedom, the spin, we have room to explore. We can explore all the possible combinations of those atoms to see which ones will be stable, and we can expand our research to realize new devices.”
When the quasiparticles spin, they feel the presence of fewer atoms, making them move faster and be more efficient. That lack of resistance prevents the device from overheating or wasting energy.
“Everything we have, from light bulbs to cars to helicopters, is based on electronic computers. In the new technology, in addition to the electrically charged properties, we are utilizing another degree of freedom—the spin of the electrons,” Singh said. “We are using both the charge and the spin together, which is why the new devices will be more energy efficient and operate much faster compared to the existing technology.”
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