Proximity-induced quasi-one-dimensional superconducting quantum anomalous Hall state

The ability to host Majorana modes, which are of great interest for more fault-tolerant quantum computation, keeps topological superconductors in the focus of research. Here, we report experimental data revealing 100-nm-wide quantum anomalous Hall insulator (QAHI) nanoribbons as a promising platform for the realization of zero-energy Majorana modes. One part of the nanoribbon is covered with superconducting niobium, while the other part is connected to a gold lead via two-dimensional QAHI regions. Andreev reflection spectroscopy reveals multiple in-gap conductance peaks in different devices. In the presence of an increasing magnetic field perpendicular to the film, the multiple-peak structure evolves into a single zero-bias conductance peak (ZBCP). Theoretical simulations suggest that the measurements are consistent with the scenario that the increasing field drives the nanoribbons from a multi-channel occupied regime to a single-channel regime, which is the necessary condition for the observation of zero-energy Majorana modes.