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Axion Insulators, Thrust Leader: N. Peter Armitage

Topological insulators are unique states of matter that – despite an insulating bulk – harbor topologically protected surface states. We are working to realize a related interacting magnetic state, the axion insulator. This is a theoretically proposed, but heretofore unrealized state of matter that is similar to a topological insulator in that both possess band inversion. However, axion insulators break time reversal symmetry and will exhibit a very large and intrinsic magnetoelectric response. For materials that preserve inversion, the magnetoelectric response is expected to be quantized. Such systems are 3D analogs of the 2D quantum anomalous Hall effect systems and should show a quantized Kerr rotation for the inversion symmetric case and a measurable (and large) dc magnetoelectric response for the inversion symmetry broken state. We have identified a very large class of potential materials and are bringing to bear the large suite of experimental tools available at IQM to realize and probe this state of matter.