Electronic structure and RPA spin susceptibility of anti-PbO type CoSe

Abstract

We report theoretical studies on bulk and monolayer CoSe with anti-PbO type structure. Using density functional theory (DFT), we find that the ferromagnetic (FM) state is energetically favored but proximity to colinear order state. Close to the Fermi level, the Co-3dxy orbital dominates the density of states (DOS). The band structure and Fermi surface reveal that both systems are in the vicinity of the Lifshitz transition. Upon hole doping, the electronic structure is found resembles that of iron-based superconductors (FeBS). Based on effective model of five Co-3d orbital for monolayer CoSe, we further perform random phase-approximation (RPA) calculation. For the undoped case, the RPA spin susceptibility has dominant peaks around (0, 0) and comparable peaks around (π, 0). Upon slight hole doping, the (π, 0) peaks are quickly enhanced and become dominant. As more holes are introduced, the spin susceptibility is found to bare extraordinary resemblance to that of FeBS. We suggest that the tetragonal CoSe may develop FM spin fluctuations due to the proximity of the Lifshitz transition. Moreover, the competition between FM and colinear order state in CoSe provides new insights into the physical properties of FeBS.