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Weyl semi-metals are a new type of material between conductors and insulators. New work by UC Davis and Chinese researchers shows that two-dimensional niobium arsenide nanobots can exhibit very high conductivity. On the left, electromagnetic transmission of niobium arsenide nanobeads manufactured in the laboratory; The right image is a higher magnification scanning EM showing the regular surface structure. The electric current can flow easily because of the quantum properties of the nanomaterial. Credit: Sergey Savrasov, UC Davis
Researchers in China and at UC Davis University have measured high conductivity in very thin layers of niobium arsenide, a type of material called Weyl semimetal. The material has a conductivity about three times that of copper at room temperature, said Sergey Savrasov, professor of physics at UC Davis. Savrasov co-authored the newspaper published on March 18 in Nature Materials.
The new materials that drive electricity are of great interest to physicists and materials scientists, both for basic research and for the development of new types of electronic devices.
Savrasov works on the theoretical physics of condensed matter. With others, he proposed the existence of Weyl semi-metals in 2011. The Chinese team was able to manufacture and test small parts, called nanobeads, niobium arsenide, thus confirming the predictions of the theory. Nanobeads are so thin that they are essentially two-dimensional.
"A Weyl semi-metal is not a conductor or an insulator, but something in between," Savrasov said. The niobium arsenide, for example, is a poor conductor en masse, but its metal surface conducts electricity. The surface is topologically protected, which means it can not be changed without destroying the bulk material.
With most materials, surfaces can be chemically modified by capturing impurities from the environment. These impurities can interfere with the conductivity. But topologically protected surfaces reject these impurities.
"In theory, we expect Weyl surfaces to be good drivers because they do not tolerate impurities," Savrasov said.
If you think of electrons going through a material, imagine them bouncing or scattering from impurities. At the quantum level, a conductive material has a Fermi surface that describes all the states of quantum energy that electrons can occupy. This Fermi surface affects the conductivity of the material.
The nanobeads tested in these experiments had a Fermi surface or a limited Fermi arc, which meant that the electrons could only be scattered over a limited range of quantum states.
"The Fermi arc limits the states on which the electrons can bounce, so they are not scattered," Savrasov said.
Highly conductive materials on a very small scale could be useful as engineers strive to build smaller and smaller circuits. Less electrical resistance means less heat is generated by current flow.
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More information:
Very high conductivity in Weyl semi-metallic nobel nanoband nanobands Nature Materials (2019). 10.1038 / s41563-019-0320-9, www.nature.com/articles/s41563-019-0320-9
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