Researchers at the U.S. Department of Energy’s Ames Laboratory, along with collaborators from Brookhaven National Laboratory and the University of Alabama at Birmingham, have found a light-induced switch that twists the crystal lattice of the material and switches on an electron current that appears to be nearly dissipationless. The discovery was made in a class of topological materials that researchers believe holds great promise for spintronics, topological effect transistors, and quantum computing. The materials in question, Weyl and Dirac semimetals, are able to host exotic, nearly dissipationless, electron conduction properties that take advantage of the unique state in the crystal lattice and electronic structure of the material. The electron transport channels, protected by symmetry and topology, typically aren’t found in conventional metals such as copper. Materials like this have been described in the context of theoretical physics, but with the advent of quantum computing, there is growing interest in materials and devices that can facilitate fragile quantum states by protecting them from impurities and noisy environments. One approach to that problem lies in the development of topological quantum computation where qubits are based on “symmetry-protected” dissipationless electric currents that are immune to noise. “Light-induced lattice twisting, or a phononic switch, can control the crystal inversion symmetry and photogenerate giant electric current with very small resistance,” said Jigang Wang, senior scientist at Ames Laboratory and professor of physics at Iowa State University. “This new control principle does not require static electric or magnetic fields and has much faster speeds and lower energy cost.” The finding, said Liang Luo, a scientist at Ames Laboratory and first author of the work’s research paper, has the potential to be extended to a novel quantum computing principle based on the chiral physics and dissipationless energy transport. That model could provide faster speeds, use less energy, and facilitate higher operational temperatures, Luo said. In using terahertz laser light spectroscopy to examine and nudge the materials into revealing the symmetry switching mechanisms, the researchers determined that to be the case. The team altered the symmetry of the material’s electronic structure by using laser pulses to twist the crystal’s lattice structure. This light switch enables “Weyl points” in the material, which cause electrons to behave as massless particles that can carry the protected, low dissipation current that the researchers had sought. “We achieved this giant dissipationless current by driving periodic motions of atoms around their equilibrium position in order to break crystal inversion symmetry,” said Ilias Perakis, professor of physics and chair at the University of Alabama at Birmingham. “This light-induced Weyl semimetal transport and topology control principle appears to be universal and will be very useful in the development of future quantum computing and electronics with high speed and low energy consumption.” Schematic of light-induced formation of Weyl points in a Dirac material of ZrTe5. Courtesy of Ames Laboratory, U.S. Department of Energy. According to Qiang Li, group leader of the Brookhaven National Laboratory’s Advanced Energy Materials Group, the researchers had previously lacked a switch that was fast enough and low energy enough to control the symmetry of such materials. “Our discovery of a light symmetry switch opens a fascinating opportunity to carry dissipationless electron current, a topologically protected state that doesn’t weaken or slow down when it bumps into imperfections and impurities in the material,” Li said. The research was published in Nature Materials (www.doi.org/10.1038/s41563-020-00882-4).