Orbital embedding and topology of one-dimensional two-band insulators

The topological invariants of band insulators are usually assumed to depend only on the connectivity between orbitals and not on their intracell position (orbital embedding), which is a separate piece of information in the tight-binding description. For example, in two dimensions, the orbital embedding is known to change the Berry curvature but not the Chern number. Here, we consider one-dimensional inversion-symmetric insulators classified by a Z2 topological invariant & thetasym; = 0 or pi, related to the Zak phase, and show that & thetasym; crucially depends on orbital embedding. We study three two-band models with bond, site, or mixed inversion: the Su-SchriefferHeeger model (SSH), the charge density wave model (CDW), and the Shockley model. The SSH (resp. CDW) model is found to have a unique phase with & thetasym; = 0 (resp. pi). However, the Shockley model features a topological phase transition between & thetasym; = 0 and pi. The key difference is whether the two orbitals per unit cell are at the same or different positions.

Automated summary

The topological invariants of one-dimensional inversion-symmetric insulators crucially depend on orbital embedding, with the position of orbitals within a unit cell playing a key role in determining the Z2 topological invariant θ. This study highlights how different orbital embedding configurations can lead to distinct topological phases in band insulators.