Predicting diamond-like Co-based chalcogenides as unconventional high temperature superconductors.

We predict Co-based chalcogenides with a diamond-like structure can host unconventional high temperature superconductivity (high-T). The essential electronic physics in these materials stems from the Co layers with each layer being formed by vertex-shared CoA (A=S, Se, Te) tetrahedra complexes, a material genome proposed recently by us to host potential unconventional high-T close to a d filling configuration in 3d transition metal compounds. We calculate the magnetic ground states of different transition metal compounds with this structure. It is found that (Mn, Fe, Co)-based compounds all have a G-type antiferromagnetic (AFM) insulating ground state while Ni-based compounds are paramagnetic metal. The AFM interaction is the largest in the Co-based compounds as the three t orbitals all strongly participate in AFM superexchange interactions. The abrupt quenching of the magnetism from the Co to Ni-based compounds is very similar to those from Fe to Co-based pnictides in which a C-type AFM state appears in the Fe-based ones but vanishes in the Co-based ones. This behavior can be considered as an electronic signature of the high-T gene. Upon doping, as we predicted before, this family of Co-based compounds favor a strong d-wave pairing superconducting state.