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.

Accepted version, to appear in Nature Communications. Main text: 16 pages, 4 figures; Supplementary Information appended (23 pages)