Side-surface-mediated hybridization in axion insulators

Abstract

We show that the half-quantized counterpropagating currents expected on the top and bottom surfaces of an axion-insulator thin film are strongly suppressed by hybridization mediated by massless side-surface states. This mechanism produces a power-law finite-size dependence rather than the exponential dependence found in conventional topological-insulator films. We further show that half quantization can be extracted in the axion insulator phase using a nonlocal transport measurement.