Superconductivity in 2D janus monolayers and bilayers

Janus transition metal dichalcogenides (J-TMDCs) is a new class of materials which shares the same honey-comb structure as graphene and conventional transition metal dichalcogenides (TMDCs) in monolayer. They have versatile physical and chemical properties which mainly feature out from their broken out of plane symmetry. This asymmetry results in an intrinsic electric field orthogonal to their plan. The presence of an intrinsic electric field gives rise to many novel properties like the Rashba effect, increased charge carrier concentration, Schottky barrier, excitons, and superconductivity. Also, they exist in multiple structural phases like, 2H, 1T, 1T' with the electrical properties shifting from semiconductor to metallic. Moreover, layer stacking and stacking pattern (AA, AB, AB', etc.) can also produce shift in their properties, like band gap tunning, and increased charge carrier concentration. Until now only a few non hydrogenated (MoSSe and WSSe) and only one hydrogenated (MoSH) J-TMDCs have been synthesized. Hence this area of research is very novel and requires a lot of simulation and experimentation for further exploration. For our work we mainly focused on hydrogenated J-TMDCs in monolayer, for their superconducting properties but as a section, non hydrogenated candidate like, TiSSe is also explored and effect of different stacking types in MoSH are also explored in detail. This work extends the studies using Density Functional Theory (DFT) implemented in QUANTUM ESPRESSO. We keep ourselves focused on ambient pressure conventional superconductors using Bardeen–Cooper–Schrieffer (BCS) theory. We explored MoSH (monolayer, Bilayer), TiSH, TiSeH, WTeH (2H, 1T), and non-hydrogenated J-TMDCs, TiSSe (1T') for ambient pressure superconductivity, out of these we successfully published TiSH and WSH, adding two more hydrogenated monolayer to total four existing. Critical temperature Tc of TiSH and WSH are reported as 9.10K and 12.2K respectively. These results were obtained from highly resolved calculations through Elais berg spectral function. We also performed calculation of self-energy for MoSH mono and bilayer. Our work emphasizes that hydrogen rich structure contributes higher frequencies which results in stronger electron-phonon coupling and this results in elevating critical temperature.