Intrinsic Higher-Order Topological States in 2d Honeycomb  [[Equation]]

Abstract

The exploration of topological phases remains a cutting-edge research frontier, driven by their promising potential for next-generation electronic and quantum technologies. In this work, we employ first-principles calculations and tight-binding modeling to systematically investigate the topological properties of freestanding two-dimensional (2D) honeycomb Bi, HgTe, and Al2O3(0001)-supported HgTe. Remarkably, all three systems exhibit coexistence of intrinsic first- and higher-order topological insulator states, induced by spin-orbit coupling (SOC). These states manifeste as topologically protected gapless edge states in one-dimensional (1D) nanoribbons and symmetry-related corner states in zero-dimensional (0D) nanoflakes. Furthermore, fractional electron charges may accumulate at the corners of armchair-edged nanoflakes. Among these materials, HgTe/Al2O3(0001) is particularly promising due to its experimentally feasible atomic configuration and low-energy corner states. Our findings highlight the importance of exploring higher-order topological phases in [[EQUATION]] quantum spin Hall insulators and pave the way for new possibilities in device applications.

Keywords: Higher-order topological insulators, two-dimensional honeycomb lattice, quantum spin Hall insulators