Topological semimetal state with triply degenerate nodal points in a stable Cu2Te structure

Abstract

Cu₂Te is commonly used as the backside contact of CdTe-based solar cells. We predict a stable topological semimetal structure of Cu₂Te(R3m) with triply degenerate nodal points near the Fermi energy. Triply degenerate nodal points are formed by the band crossing between two states with angular momentum j equal to 3/2 and 1/2 along the unique C₃ axis. The anisotropic strain breaking C₃ symmetry opens the energy gap, and transforms semimetal Cu₂Te(R3m) into a topological insulator. It provides strong evidence for understanding the unconventional large linear magnetoresistance in Cu_2−xTe. The band crossing of Cu₂Te(R3m) strongly depends on the orbital on-site energy difference and the SOC strength. Crystal structures with the space group R3m (no. 160) are a good platform to obtain topological semimetals with triply degenerate nodal points. Compounds X₂Y (X = Cu, Ag, Au, Y = O, S, Se, Te) except for Au₂S and Cu₂O are topological semimetals with triply degenerate nodal points around the Fermi energy.