Converting topological insulators into topological metals within the tetradymite family

International audienceWe report the electronic band structures and concomitant Fermi surfaces for a family of exfoliable tetradymite compounds with the formula T 2 C h 2 P n , obtained as a modification to the well-known topological insulator binaries Bi 2 ( Se , Te ) 3 by replacing one chalcogen ( C h ) with a pnictogen ( P n ) and Bi with the tetravalent transition metals T = Ti, Zr, or Hf. This imbalances the electron count and results in layered metals characterized by relatively high carrier mobilities and bulk two-dimensional Fermi surfaces whose topography is well-described by first-principles calculations. Intriguingly, slab electronic structure calculations predict Dirac-like surface states. In contrast to Bi 2 Se 3 , where the surface Dirac bands are at the Γ point, for ( Zr , Hf ) 2 Te 2 (P,As) there are Dirac cones of strong topological character around both the ¯¯¯ Γ and ¯¯¯¯ M points, which are above and below the Fermi energy, respectively. For Ti 2 Te 2 P , the surface state is predicted to exist only around the ¯¯¯¯ M point. In agreement with these predictions, the surface states that are located below the Fermi energy are observed by angle-resolved photoemission spectroscopy measurements, revealing that they coexist with the bulk metallic state. Thus this family of materials provides a foundation upon which to develop novel phenomena that exploit both the bulk and surface states (e.g., topological superconductivity)