Strong-coupling superconductivity with Tc ∼ 10.8 K induced by P doping in the topological semimetal Mo5Si3

Abstract

By performing P doping on the Si sites in the topological semimetal Mo5Si3, we discover strong-coupling superconductivity in Mo5Si3−xPx (0.5 ≤ x ≤ 2.0). Mo5Si3 crystallizes in the W5Si3-type structure with space group of I4/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 Mo5Si3−xPx (0.5 ≤ x ≤ 2.0) from resistivity, magnetization, and heat capacity measurements. Tc in Mo5Si1.5P1.5 reaches as high as 10.8 K, setting a new record among the W5Si3-type superconductors. The upper and lower critical fields for Mo5Si1.5P1.5 are 14.56 T and 105 mT, respectively. Moreover, Mo5Si1.5P1.5 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 Mo5Si3. The Tc and upper critical field in Mo5Si3−xPx are fairly high among pseudobinary compounds. Both of them are higher than those in NbTi, making future applications promising. Our results suggest that the W5Si3-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.