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Speaker: David Vanderbilt
"Axion Insulators and Surface Quantum Point Junctions"
Strong topological insulators in 3D exhibit a quantized orbital magnetoelectric "axion" coupling, which is reflected in the presence of a half-integer quantum anomalous Hall (QAH) response on any gapped surface. However, unless time-reversal symmetry is broken at the surface, this response is hidden by the surface metallicity. By contrast, in axion insulators the quantized axion coupling is protected by inversion; since this is not a symmetry at any surface, the surface are naturally gapped, exposing the surface QAH response and associated chiral edge channels. Similar physics arises in antiferromagnetic topological insulators. While 3D materials realizations are still an object of active search, I will look ahead to discuss future opportunities presented by such materials, including the possible manipulation of surface chiral channels to form novel quantum point junctions that can perform qubit operations.