(Left) Transmission electron microscope image of niobium arsenide nanobelts fabricated in the lab; (right) a higher magnification scanning electron microscope image showing the regular surface structure of the nanobelts. Electrical current can flow easily because of the quantum properties of the nanomaterial. Image: Sergey Savrasov, UC Davis.Researchers at the University of California (UC) Davis, together with colleagues in China, have measured high conductivity in very thin layers of niobium arsenide, a type of material called a Weyl semimetal. This material has about three times the conductivity of copper at room temperature, said Sergey Savrasov, professor of physics at UC Davis. Savrasov is a coauthor of a paper on this work in Nature Materials.
New materials that conduct electricity are of great interest to physicists and materials scientists, both for basic research and because they could lead to new types of electronic devices.
Savrasov works on theoretical condensed matter physics. With others, he proposed the existence of Weyl semimetals in 2011. The Chinese team were able to fabricate and test small pieces, called nanobelts, of niobium arsenide, confirming the predictions of theory. The nanobelts are so thin they are essentially two-dimensional.
"A Weyl semimetal is not a conductor or an insulator, but something in between," Savrasov said. Niobium arsenide, for example, is a poor conductor in bulk but has a metallic surface that conducts electricity. The surface is topologically protected, meaning that it cannot be changed without destroying the bulk material.
With most materials, surfaces can be chemically altered as they pick up impurities from the environment. These impurities can interfere with conductivity. But topologically protected surfaces reject these impurities. "In theory we expect Weyl surfaces to be good conductors as they don't tolerate impurities," Savrasov said.
If you think of electrons flowing through material, imagine them bouncing off or scattering from impurities. At the quantum level, a conductive material has a Fermi surface that describes all the quantum energy states that electrons can occupy, which affects the conductivity of the material. The nanobelts tested in these experiments had a limited Fermi surface or Fermi arc, meaning that electrons could only be scattered to a limited range of quantum states.
"The Fermi arc limits the states electrons can bounce back to, therefore they are not scattered," Savrasov said.
Materials that are highly conductive at very small scales could be useful as engineers strive to build smaller and smaller circuits. Less electrical resistance means that less heat is generated as current passes through.
This story is adapted from material from the University of California Davis, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.