Large gap high-order topological insulators in superatomic graphene*

High-order topological insulators (HOTIs) have been investigated in several two-dimensional (2D) lattices. The inter and intra-hexagon hopping in a Kekulé lattice opens a non-trivial gap protected by the lattice symmetry, leading to the zero-dimensional corner states. However, the realization of the 2D HOTI is still challenging because of the limit of material candidates and the weak signal of the corner states. Here, we introduce the on-site Coulomb repulsion (U) in the Kekulé lattice to enlarge the topological gap. We found that the corner states become more localized, and the intensity of the corner mode is significantly enhanced. We further proposed a series of superatomic graphene lattices superimposed on a Kekulé lattice for the realization of large gap HOTIs with different U/t ratios. Our results provide a promising strategy to generate strong topological corner states.