Laughlin charge pumping in a quantum anomalous Hall insulator

The adiabatic charge pump is one of the most salient features of topological phases of matter. By threading a magnetic flux quantum through a cylinder of quantum Hall insulator, an electron is pumped along the cylinder axis. This phenomenon is known as the Laughlin charge pumping. In analogy to the quantum Hall insulator, the quantum anomalous Hall insulator of a cylinder geometry is predicted to induce the Laughlin charge pump by threading magnetic fluxes through the cylinder [1,2]. We experimentally observed the Laughlin charge pump in a thin-film magnetic heterostructure of topological insulators in a sample with a Corbino disk geometry [3]. We find that charges are pumped between the inner and outer electrodes of the Corbino disk in response to alternating magnetic fields. We also find the charge pumping does not occur in the axion insulator phase where the magnetization directions for the top and bottom surfaces are opposite to each other. The amount of the pumped charge is accounted for by the surface Hall conductivity of half the quantum conductance for each surface. Because there are no edge channels connecting the electrodes in the Corbino geometry, our observation directly indicates that the current is carried by the surface instead of the edges.

[1] D. -H. Lee, Phys. Rev. Lett. 103, 196804 (2009).

[2] O. Vafek et al., Phys. Rev. B 84, 245417 (2011).

[3] M. Kawamura et al., Nat Phys. 19, 333 (2023).