New classes of topological crystalline insulators with unpinned surface Dirac cones

TL;DR

This paper predicts two new classes of three-dimensional topological crystalline insulators with unpinned surface Dirac cones, protected by specific crystal symmetries, expanding the understanding of topological phases beyond existing models.

Contribution

The authors introduce two novel classes of TCIs protected by glide plane and rotation-time reversal symmetries, characterized by a quantized Berry phase and a $Z_2$ invariant, with potential material realizations.

Findings

Surface states are protected against localization by crystal symmetries.

Surface Dirac cones are unpinned and protected by specific symmetries.

Existence of these TCIs in time-reversal-breaking systems with or without spin-orbit coupling.

Abstract

We theoretically predict two new classes of three-dimensional topological crystalline insulators (TCIs), which have an odd number of unpinned surface Dirac cones protected by crystal symmetries. The first class is protected by a single glide plane symmetry; the second class is protected by a composition of a twofold rotation and time-reversal symmetry. Both classes of TCIs are characterized by a quantized $\pi$ Berry phase associated with surface states and a $Z_2$ topological invariant associated with the bulk bands. In the presence of disorder, these TCI surface states are protected against localization by the average crystal symmetries, and exhibit critical conductivity in the universality class of the quantum Hall plateau transition. These new TCIs exist in time-reversal-breaking systems with or without spin-orbital coupling, and their material realizations are discussed.