Gapless hinge states from adiabatic pumping of axion coupling

Abstract

We demonstrate that chiral hinge modes naturally emerge in insulating crystals undergoing a slow cyclic evolution that changes the Chern-Simons axion angle $\theta$ by $2\pi$. This happens when the surface (not just the bulk) returns to its initial state at the end of the cycle, in which case it must pass through a metallic state to dispose of the excess quantum of surface anomalous Hall conductivity pumped from the bulk. If two adjacent surfaces become metallic at different points along the cycle, there is an interval in which they are in topologically distinct insulating states, with chiral modes propagating along the connecting hinge. We illustrate these ideas for a tight-binding model consisting of coupled layers of the Haldane model with alternating parameters. The surface topology is determined in a slab geometry using two different markers, surface anomalous Hall conductivity and surface-localized charge pumping (flow of surface-localized Wannier bands), and we find that both correctly predict the appearance of gapless hinge modes in a rod geometry. When viewing the axion pump as a four-dimensional (4D) crystal with one synthetic dimension, the hinge modes trace Fermi arcs in the Brillouin zone of the 2D hinge connecting a pair of 3D surfaces of the 4D crystal.

arXiv comment11 pages, 11 figures

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Cited by in corpus (5)

• Axionic Band Topology in Inversion-Symmetric Weyl-Charge-Density Waves
• Direct dynamical characterization of higher-order topological insulators with nested band inversion surfaces
• Quantized surface magnetism and higher-order topology: Application to the Hopf insulator
• Protected Gapless Edge States In Trivial Topology
• Simulating Higher-Order Topological Insulators in Density Wave Insulators