Magnetic-field induced s+ if pairing in Ising superconductors

We show that an in-plane Zeeman field applied to noncentrosymmetric Ising superconductors converts singlet s-wave Cooper pairs to equal-spin triplet if pairs. Singlets are converted to triplets as spins originally polarized by spin-orbit interaction are reoriented by the Zeeman field. We demonstrate that the pairing in the triplet f channel(s) decisively affects the critical field. While attraction enhances the critical field, repulsion suppresses it. The singlet to triplet conversion phenomenon has a geometrical origin, and the discussion applies universally to Ising superconductors with generic band structure such as, e.g., monolayer transition metal dichalcogenides.