Emergence of superconductivity in (NH₃)_y M_xMoSe₂ (M: Li, Na and K)

We report syntheses of new superconducting metal-doped MoSe₂ materials (M_xMoSe₂). The superconducting M_xMoSe₂ samples were prepared using a liquid NH₃ technique, and can be represented as '(NH₃)_yM_xMoSe₂'. The T_cs of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH₃)_yNa_xMoSe₂ were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe₂ layers. The x-independence of c was observed in (NH₃)_yNa_xMoSe₂, 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 MoSe₂ with Li and K also yielded superconductivity. Thus, MoSe₂ is a promising material for designing new superconductors, as are other transition metal dichalcogenides.