Higher-order topological and nodal superconducting transition-metal sulfides MS (M=Nb and Ta)

Intrinsic topological superconducting materials are exotic and vital to develop the next-generation topological superconducting devices, topological quantum calculations, and quantum information technologies. Here, we predict the topological and nodal superconductivity of NiAs-type $M\mathrm{S}$ $(M=\mathrm{Nb}\text{and}\mathrm{Ta})$ transition-metal sulfides. We reveal their higher-order topology nature with an index of ${Z}₄=2$. These materials have a higher ${T}_{\mathrm{c}}$ than the Nb or Ta metal superconductors due to their flat band and strong electron-phonon coupling nature. Electron doping and lighter isotopes can effectively enhance the ${T}_{\mathrm{c}}$. Our findings show that the $M\mathrm{S}$ $(M=\mathrm{Nb}\text{and}\mathrm{Ta})$ systems can be platforms to study exotic physics in the higher-order topological superconductors, and provide a theoretical support to utilize them as the topological superconducting devices in the field of advanced topological quantum calculations and information technologies.