Hidden breathing kagome topology in hexagonal transition metal dichalcogenides

Abstract

A kagome lattice, formed by triangles of two different directions, is known to have many emergent quantum phenomena. Under the breathing anisotropy of bond strengths, this lattice can become a higher-order topological insulator (HOTI), which hosts topologically protected corner states. Experimental realizations of HOTI on breathing kagome lattices have been reported for various artificial systems, but not for simple natural materials with an electronic breathing kagome lattice. Here we prove that a breathing kagome lattice and HOTI are hidden inside the electronic structure of hexagonal transition metal dichalcogenides (h-TMD). Due to the trigonal prismatic symmetry, $s{p}^{2}$-like hybrid $d$ orbitals create an electronic kagome lattice with anisotropic intersite and on-site hopping interactions. We demonstrate that HOTI h-TMD triangular nanoflakes host topologically protected corner states, which could be quantum-mechanically entangled with triple degeneracy. Because $\mathrm{h}\text{\ensuremath{-}}\mathrm{TM}{\mathrm{D}}_{\mathrm{S}}$ are easily synthesizable and stable with a large bandgap at ambient conditions, our findings open an avenue for quantum physics based on simple condensed matter systems.