Laughlin charge pumping from interplay of chiral Dirac and chiral Majorana modes

Abstract: Laughlin charge pumping has provided critical insights into the topological classification of individual materials, but remains largely unexplored in topological junctions. We explore Laughlin charge pumping in junctions composed of a chiral topological superconductor sandwiched between two quantum anomalous Hall insulators, driven by an adiabatically varying magnetic flux. Here, charge pumping can be mediated merely by chiral Dirac modes or by the interplay of chiral Dirac and chiral Majorana modes (CMMs). In the former case, a variation of one magnetic flux quantum induces the pumping of a unit charge, as the chiral Dirac mode accumulates the full flux-induced phase. In contrast, in the latter case, pumping a unit charge requires a variation of fractional magnetic flux quanta, determined by the device geometry and the parity of the number of enclosed superconducting vortices. This unique feature results from the charge-neutral and zero-momentum nature of zero-energy CMMs. Our work offers an experimentally viable pathway toward detecting CMMs and could also inspire further research into Laughlin charge or spin pumping in diverse topological junctions, which are now within experimental reach.