Laughlin charge pumping in a quantum anomalous Hall insulator

Adiabatic charge pumping is one of the most salient features of topological phases of matter(1-3). Laughlin's charge pumping in a quantum Hall system is the prototypical example(4). In analogy, three-dimensional topological insulators have been predicted to support charge pumping through their magnetically gapped surface states(5-10). But despite its importance as a direct probe of surface Hall conductivity, charge pumping has not been demonstrated in topological-insulator-based systems. Here we report the observation of charge pumping in a thin-film magnetic heterostructure of topological insulators in a geometry that prohibits edge transport. We find that charge pumping occurs between the inner and outer electrodes in response to alternating magnetic fields when the sample is in the quantum anomalous Hall insulator phase. The amount of pumped charge is accounted for by the surface Hall conductivity of half the quantum conductance for each surface, from a comparison with the axion insulator phase that shows no charge pumping. Because charge pumping is closely related to the theoretically predicted topological magnetoelectric effect(5-10), our observation may provide clues to its direct observation. Quantized charge pumping is a hallmark of topological phases. Now, this effect is observed in the quantum anomalous Hall regime.