Theoretical prediction of superconductivity and nontrivial band topology in rock-salt transition-metal hydrides MH (M = Mo, W, Ru, Rh, Y)

Transition-metal hydrides have recently emerged as a promising platform for exploring the interplay between super-conductivity and nontrivial band topology. Here, using first-principles calculations, we predict a family of rock-salt transition-metal monohydrides MH (M = Mo, W, Ru, Rh, Y) that are stable at ambient pressure. Our calculations show that these compounds exhibit phonon-mediated superconductivity, with estimated superconducting transition temperatures of 14.6 K, 14.5 K, 5.3 K, 7.9 K, and 4.5 K for MoH, WH, RuH, RhH, and YH, respectively. For MoH and WH, the electron-phonon coupling is mainly contributed by the softened low-frequency phonon modes associated with transition-metal vibrations, which couple strongly to the doubly degenerate d-orbitals (d_x²-y² and d_z²) near the Fermi level. In addition, spin-orbit coupling opens nontrivial band gaps near the Fermi level, as confirmed by Z₂ topological invariants and topologically protected surface states. These results identify rock-salt transition-metal monohydrides as promising ambient-pressure platforms for investigating the coexistence of superconductivity and nontrivial band topology.