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

基于简并p轨道的平带模型及其二维材料实现

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 1 T 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., K2 S), and some of the latter have been experimentally fabricated in previous works(e.g., Gd2 CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2 S monolayer and graphene layers. The spin polarized nearly flatband can be realized in the ferromagnetic state of a Gd2 CCl2 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.

作为一种无色散且态密度发散的电子结构,平带为研究相互作用、实现新奇物理性质提供了理想平台.设计理论模型并寻找相应的材料实现受到了广泛关注.当前,基于现有理论模型寻找和制备具有理想平带的二维材料仍存在不同程度的挑战.本文提出了一种可以在一系列二维材料中实现平带的新型理论模型.以结构稳定的硫化钾(K2S)二维单层为例,其平带的色散仅为50毫电子伏左右.在硫化钾单层与石墨烯构成的异质结中,层间的电荷转移可以调节平带的部分填充.该平带模型还可以在一些1T结构的三元化合物中实现.例如,已经被实验室合成的Gd2CCl2.第一性原理计算表明,在铁磁态的Gd2CCl2单层中,还可以实现自旋极化的平带.此文提出的理论模型与二维材料为平带以及相关新奇物理性质的研究提供了理想的且可实现的平台.