Higher-order topological corner states and origin in monolayer LaBrO

Intrinsic higher-order topological insulators driven solely by orbital coupling are rare in electronic materials. Here, we propose that monolayer LaBrO is an intrinsic two-dimensional second-order topological insulator. The generalized second-order topological phase arises from the coupling between the 5d orbital of the La atom and the 2p orbital of the O atom. The underlying physics can be thoroughly described by a four-band generalized higher-order topological model. Notably, the edge states and corner states of monolayer LaBrO exhibit different characteristics in terms of morphology, number, and location distribution under different boundary and nanocluster configurations. Furthermore, the higher-order topological corner states of monolayer LaBrO are robust against variations in spin–orbit coupling and different values of Hubbard U. This provides a material platform for studying intrinsic 2D second-order topological insulators.