A new type of semimetal has been proven to exist in a crystal made of molybdenum and tellurium atoms. In this recently postulated state, the electron and hole bands normally separated by a gap touch at a few discrete points, called Weyl points. The orientation of electron spin at those points in momentum space resembles magnetic field lines of magnetic monopoles. Weyl points are connected by “Fermi arcs” at the surface of the sample, which allow their identification. Fermi arcs are disconnected, ungapped areas in density of states of these materials. The proof of the existence of this new semimetal required both careful measurements and calculations to detect the Weyl points and Fermi arcs. Angle resolved photoemission spectroscopy identified the Fermi arcs, confirming the new type of Weyl semimetal. This material opens the way to study Weyl fermions, a type of massless elementary particle hypothesized by high-energy particle theorists and long sought after experimentally. The discovery has implications for the discovery of more new materials with unusual transport properties for quantum computing and ultrafast electronics.
Constant energy intensity contour 10 meV above EF in the momentum space. White, gray and green are locations of the bands. points. Theoretically predicted locations for the Weyl points (green) and the experimentally determined points (red). Fermi arcs are seen as white strikes of intensity connecting “experimental” Weyl points.
Spectroscopic Evidence for a Type II Weyl Semimetallic State in MoTe2