Superconductivity in Mo 4 Ga 20 As with endohedral gallium clusters.

We report the discovery and detailed investigation of superconductivity in Mo 4 Ga 20 As. Mo 4 Ga 20 As crystallizes in a space group of I 4/ m (No. 87), with the lattice parameters a = 12.86352 Å and c = 5.30031 Å. The resistivity, magnetization, and specific heat data reveal Mo 4 Ga 20 As to be a type-II superconductor with T c = 5.6 K. The upper and lower critical fields are estimated to be 2.78 T and 22.0 mT, respectively. In addition, electron-phonon coupling in Mo 4 Ga 20 As is possibly stronger than the BCS weak-coupling limit. First-principles calculations suggest the Fermi level being dominated by the Mo-4 d and Ga-4 p orbitals.