Emergence of superconductivity in (NH 3 ) y M x MoSe 2 (M: Li, Na and K)

We report syntheses of new superconducting metal-doped MoSe 2 materials (M x MoSe 2 ). The superconducting M x MoSe 2 samples were prepared using a liquid NH 3 technique and can be represented as ‘(NH 3 ) y M x MoSe 2 ’. The T c s of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH 3 ) y Na x MoSe 2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe 2 layers. The x-independence of c was observed in (NH 3 ) y Na x MoSe 2 , indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of T c . A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe 2 with Li and K also yielded superconductivity. Thus, MoSe 2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.