Machine learning accelerated discovery of superconducting two-dimensional Janus transition metal sulfhydrates

The MoSH monolayer, one of the Janus transition metal sulfhydrates synthesized by stripping the top-layer S of MoS₂ and replacing it with H atoms Wan et al. , ACS Nano 15, 20319 (2021), has been predicted to host strong coupling two-gap superconductivity with a calculated critical temperature T₂ of about 28. 58 K at atmospheric pressure. In this work, by using machine learning aided high-throughput calculations, we narrow down 180 possible configurations of two-dimensional Janus transition metal sulfhydrates (MXH monolayers, where M=transition metal group elements and X=S, Se, and Te) to 20 stable metals. Among them, we identify six low-energy monolayers that are potential high-T₂ superconductors. Notably, the 1T-TiSH monolayer stands out with the highest T₂ of approximately 48 K, surpassing the superconducting properties of 1H-MoSH (T₂=28. 58 K) and the well-known MgB₂ superconductor (T₂=39 K). By solving the anisotropic Migdal-Eliashberg equations, we find that 1T-TiSH naturally exhibits a one-gap superconducting nature with strong electron-phonon coupling (=2. 79) originating from the interactions of Ti dₗₙ, ₘₙ orbitals and in-plane vibrations, which is different from and better than the 1H-MoSH monolayer (=1. 60). The presented results enrich families of Janus transition metal sulfhydrates and accelerate the design of novel two-dimensional superconductors.