Visualizing currents in the quantum anomalous Hall regime

We report a magnetic imaging study of the current distribution in the quantum anomalous Hall regime. We use a scanning superconducting quantum interference device (SQUID) microscope with micrometer scale spatial resolution to image the magnetic fields above Cr-doped (Bi,Sb)2Te3 samples. From these data we reconstruct the local current density, allowing us to visualize how current flows in our devices. Surprisingly, we find that most current flows in the bulk when the transport coefficients are quantized. By combining this observation with images of the equilibrium persistent currents, we construct a comprehensive picture of electronic transport in the quantum anomalous Hall regime.