Ab Initio Investigations of Kagome Xenes

Materials with dispersionless electronic states (or flat bands) have been intensely investigated in recent years, owing to their association with strongly correlated electrons. Due to the negligible kinetic energies of electrons in such states, the electron-electron interaction dominates, thus resulting in superconductivity, ferromagnetism, and other exotic phases of matter, as exemplified famously by twisted bilayer graphene. However, the discovery of new low-dimensional flat band materials, especially elemental ones, remains a challenge. First principles calculations based on Density functional theory (DFT) have shown recently that the 2-dimensional carbon kagome lattice is structurally stable and has a flat band around its Fermi level. Here, in order to seek novel stable elemental 2D materials with flat bands, we utilize DFT to systematically study other Group IVA elements, in Kagome lattice configurations. We show that these Kagome Xenes (X = C, Si, Ge, Sn, Pb) all generically support flat bands, but unlike their carbon counterpart, they do not prefer planar structures. We discuss various electro-mechanical properties of these materials and provide contrasts with the corresponding classical hexagonal-lattice Xenes (i.e., silicene, germanene, stanine and plumbene).