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

Cu 2 Te is commonly used as the backside contact of CdTe-based solar cells. We predict a stable topological semimetal structure of Cu 2 Te( R 3 m ) 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 C 3 axis. The anisotropic strain breaking C 3 symmetry opens the energy gap, and transforms semimetal Cu 2 Te( R 3 m ) into a topological insulator. It provides strong evidence for understanding the unconventional large linear magnetoresistance in Cu 2− x Te. The band crossing of Cu 2 Te( R 3 m ) strongly depends on the orbital on-site energy difference and the SOC strength. Crystal structures with the space group R 3 m (no. 160) are a good platform to obtain topological semimetals with triply degenerate nodal points. Compounds X 2 Y (X = Cu, Ag, Au, Y = O, S, Se, Te) except for Au 2 S and Cu 2 O are topological semimetals with triply degenerate nodal points around the Fermi energy. We predict a stable topological structure of Cu 2 Te( R 3 m ) with triply degenerate nodal points near the Fermi energy. The anisotropic strain breaking C 3 symmetry turns the semimetal into a topological insulator, providing evidence for the large linear magnetoresistance in Cu 2− x Te.