Topological superconductivity in Janus monolayer transition metal dichalcogenides

The Janus monolayer transition metal dichalcogenides (TMDs) MXY (M=\rm Mo, W, etc. and X, Y=\rm S, Se, etc.) have been successfully synthesized in recent years. The Rashba spin splitting in these compounds arises due to the breaking of out-of-plane mirror symmetry. Here we study the pairing symmetry of superconducting Janus monolayer TMDs within the weak-coupling framework near critical temperature T_\rm c, of which the Fermi surface (FS) sheets centered around both ărGamma and K (K') points. We find that the strong Rashba splitting produces two kinds of topological superconducting states which differ from that in its parent compounds. More specifically, at relatively high chemical potentials, we obtain a time-reversal invariant s + f + p-wave mixed superconducting state, which is fully gapped and topologically nontrivial, i.e., a \mathbbZ_2 topological state. On the other hand, a time-reversal symmetry breaking d + p + f-wave superconducting state appears at lower chemical potentials. This state possess a large Chern number |C|=6 at appropriate pairing strength, demonstrating its nontrivial band topology. Our results suggest the Janus monolayer TMDs to be a promising candidate for the intrinsic helical and chiral topological superconductors.