Orbital shift-induced boundary obstructed topological materials with a large energy gap

TL;DR

This paper introduces boundary obstructed topological phases caused by Wannier orbital shifts, predicting new materials with large energy gaps and boundary states that are experimentally detectable, expanding the understanding of topological insulators.

Contribution

It proposes a new class of boundary obstructed topological phases driven by orbital shifts, identifying eight overlooked materials with large energy gaps and boundary states.

Findings

Predicted eight new boundary obstructed topological insulators.

Materials exhibit large energy gaps over 1 eV.

Materials also identified as fragile topological insulators.

Abstract

We propose boundary obstructed topological phases caused by Wannier orbital shift between ordinary atomic sites, which, however, cannot be indicated by symmetry eigenvalues at high symmetry momenta (symmetry indicators) in bulk. On the open boundary, Wannier charge centers can shift to different atoms from those in bulk, leading to in-gap surface states, higher-order hinge states or corner states. To demonstrate such orbital-shift-induced boundary obstructed topological insulators, we predict eight material candidates, all of which were overlooked in present topological databases. Metallic surface states, hinge states, or corner states cover the large bulk energy gap (for example, more than 1 eV in TlGaTe$_2$) at related boundary, which are ready for experimental detection. Additionally, we find these materials are also fragile topological insulators with hourglass like surface states.