Crystalline topological states at a topological insulator junction

TL;DR

This paper investigates the electronic states at the interface between two topological insulators with opposite surface state chirality, revealing mirror-symmetry-protected gapless modes and their sensitivity to rotational mismatch.

Contribution

It introduces a continuum model for topological insulator interfaces that captures symmetry effects and predicts protected gapless states, supported by ab initio parameterization.

Findings

Interface supports mirror-symmetry-protected gapless modes

Rotational mismatch can open a gap in the interface states

Model accurately describes Bi2Se3 class topological insulators

Abstract

We consider an interface between two strong time-reversal invariant topological insulators having surface states with opposite spin chirality, or equivalently, opposite mirror Chern number. We show that such an interface supports gapless modes that are protected by mirror symmetry. The interface states are investigated with a continuum model for the Bi2Se3 class of topological insulators that takes into account terms up to third order in the crystal momentum, which ensures that the model has the correct symmetry. The model parameters are obtained from ab initio calculations. Finally, we consider the effect of rotational mismatch at the interface, which breaks the mirror symmetry and opens a gap in the interface spectrum.