Nodal Brillouin Zone Boundary from Folding a Chern Insulator

TL;DR

This paper introduces a novel insulator formed by folding a Chern insulator's spectrum, resulting in a nodal boundary in the Brillouin zone and unique topological properties influenced by nonsymmorphic symmetries.

Contribution

It presents a new class of insulator with a folded spectrum and symmetry-protected nodal boundary, expanding the understanding of topological phases and Berry curvature effects.

Findings

Folding of Chern insulator spectrum creates a nodal boundary.

Nonsymmorphic symmetries distinguish the two underlying Chern insulators.

Topological pumping involves a parity degree of freedom related to nonsymmorphic symmetry.

Abstract

Chern insulator is a building block of many topological quantum matters, ranging from quantum spin Hall insulators to fractional Chern insulators. Here, we discuss a new type of insulator, which consists of two half filled ordinary Chern insulators. On the one hand, the bulk energy spectrum is obtained from folding that of either Chern insulator. Such folding gives rise to a nodal boundary of the Brillouin zone, at which the band crossing is protected by the symmetries of the two-dimensional lattice that is invariant under combined transformations in the spatial and the spin space. It also provides one a natural platform to explore the non-abelian Berry curvature and the resultant quantum phenomena. On the other hand, these two underlying Chern insulators are distinguished from each other by nonsymmorphic operators, which lead to intriguing properties absent in conventional Chern insulators. A new degree of freedom, the parity of the nonsymmorphic symmetry, needs to be introduced for describing the topological pumping, if the edge respects the nonsymmorphic symmetry.