Antiferromagnetic topological insulators

Understand

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.