Observation of Quantized Charge Accumulation in a Quantum Anomalous Hall System

Abstract

The quantum anomalous Hall effect in magnetically doped topological insulators exhibits a quantized Hall conductance $\sigma_{xy} = e^2/h$ 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 $\sigma_{xy}$. 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 $\Delta B$, with dissipation characterized by longitudinal conductance $\sigma_{xx}$ and frequency $f$. A quantitative dissipation model extracts the intrinsic quantized charge density $\eta_0 = (e^2/h)\Delta B$, which is confirmed through $f$- and $\sigma_{xx}$-dependent measurements. Under ultra-low dissipation ($\sigma_{xx} \approx 10^{-9}$ 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.