Antiferromagnetic topological insulators

TL;DR

This paper explores antiferromagnetic topological insulators characterized by a combined symmetry leading to a Z2 classification, revealing unique surface states and potential experimental signatures like half-quantum Hall effects.

Contribution

It introduces the concept of antiferromagnetic topological insulators protected by combined symmetry, expanding the classification of topological phases beyond time-reversal symmetry.

Findings

Identification of a Z2 topological classification for antiferromagnets with combined symmetry

Prediction of gapped surface states with half-quantum Hall effect

Discussion of GdBiPt as a candidate material

Abstract

We consider antiferromagnets breaking both time-reversal (Theta) and a primitive lattice translational symmetry (T) of a crystal but preserving the combination S = Theta T. The S symmetry leads to a Z_2 topological classification of insulators, separating the ordinary insulator phase from the "antiferromagnetic topological insulator" (AFTI) phase. This state is similar to the "strong" topological insulator with time-reversal symmetry, and shares with it such properties as a quantized magnetoelectric effect. However, for certain surfaces the surface states are intrinsically gapped with a half-quantum Hall effect (sigma_{xy} = e^2 / 2h), which may aid experimental confirmation of theta = pi quantized magnetoelectric coupling. Step edges on such a surface support gapless, chiral quantum wires. In closing we discuss GdBiPt as a possible example of this topological class.