Corner states, energy spectrum and light absorption of γ−graphyne quantum dots

Recently, γ−graphyne has been recognized as a two-dimensional high-order topological insulator with typical corner states. In this work, we examine the condition for the existence of corner states in a hexagonal quantum dot made of γ−graphyne (GYQD). Based on a single-orbital tight-binding model, we find that corner states appear only when there are partially-bonding carbon atoms located at the corners. This indicates a potential instability of corner states. As the size of GYQDs increases, mid-gap states in the energy spectrum are either prohibited or exhibited as corner-only or edge-only states. Additionally, we find that the light absorption of GYQDs has a relatively weak polarization anisotropy. The presence of corner states leads to the emergence of sub-gap absorption and enhancement of above-gap absorption.