Observation of quantized charge accumulation in a quantum anomalous Hall system

The quantum anomalous Hall effect in magnetically doped topological insulators exhibits a quantized Hall conductance σxy = e2/h arising from the two-dimensional surface states. While conventional transport probes confirm this quantization, they remain insensitive to the field-induced surface charge accumulation as a direct manifestation of σxy. Here, we experimentally validate an out-of-plane capacitive method that directly detects this quantized charge accumulation in a quantum anomalous Hall system. Using Corbino and simple disk devices, we measure charge accumulation proportional to field variation ΔB, with dissipation characterized by longitudinal conductance σxx and frequency f. A quantitative dissipation model extracts the intrinsic quantized charge density η0 = (e2/h)ΔB, which is confirmed through f- and σxx-dependent measurements. Under ultra-low dissipation (σxx ≈ 10−9 S), we directly resolve the fully quantized charge accumulation. This methodology establishes a direct charge-accumulation probe and provides a pathway toward detecting the topological magnetoelectric effect, a condensed matter manifestation of the four-dimensional quantum Hall effect. The quantum anomalous Hall effect in a magnetically doped topological insulator exhibits a quantized Hall conductance. Here, the authors demonstrate an out-of-plane capacitive method that directly measures field-induced quantized charge accumulation originating from the quantized Hall conductance.