Strong-coupling superconductivity with T c ∼ 10.8 K induced by P doping in the topological semimetal Mo 5 Si 3

By performing P doping on the Si sites in the topological semimetal Mo 5 Si 3 , we discover strong-coupling superconductivity in Mo 5 Si 3− x P x (0.5 ≤ x ≤ 2.0). Mo 5 Si 3 crystallizes in the W 5 Si 3 -type structure with space group of I 4/ mcm (No. 140), and is not a superconductor itself. Upon P doping, the lattice parameter a decreases while c increases monotonously. Bulk superconductivity is revealed in Mo 5 Si 3− x P x (0.5 ≤ x ≤ 2.0) from resistivity, magnetization, and heat capacity measurements. T c in Mo 5 Si 1.5 P 1.5 reaches as high as 10.8 K, setting a new record among the W 5 Si 3 -type superconductors. The upper and lower critical fields for Mo 5 Si 1.5 P 1.5 are 14.56 T and 105 mT, respectively. Moreover, Mo 5 Si 1.5 P 1.5 is found to be a fully gapped superconductor with strong electron-phonon coupling. First-principles calculations suggest that the enhancement of electron-phonon coupling is possibly due to the shift of the Fermi level, which is induced by electron doping. The calculations also reveal the nontrivial band topology in Mo 5 Si 3 . The T c and upper critical field in Mo 5 Si 3− x P x are fairly high among pseudobinary compounds. Both of them are higher than those in NbTi, making future applications promising. Our results suggest that the W 5 Si 3 -type compounds are ideal platforms to search for new superconductors. By examinations of their band topologies, more candidates for topological superconductors can be expected in this structural family.