Realistic flat-band model based on degenerate p-orbitals in two-dimensional ionic materials

Abstract Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principles calculations show that the proposed flat-band can be realized in 1T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials (e.g., K2S), and some of the latter have been experimentally fabricated in previous works (e.g., Gd2CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2S monolayer and graphene layers. The spin polarized nearly flat-band can be realized in the ferromagnetic state of a Gd2CCl2 monolayer, which has been fabricated in experiments. Our theoretical model together with the material predictions provide a realistic platform for the study of flat-bands and related exotic quantum phases.