Tunneling spectroscopy of Andreev bands in multiterminal graphene-based Josephson junctions.

Multiply connected electronic networks threaded by flux tubes have been proposed as a platform for adiabatic quantum transport and topological states. Multiterminal Josephson junction (MTJJ) has been suggested as a pathway to realize this concept. Yet, the manifestations of topology in MTJJ remain open for experimental study. Here, we investigated the artificial topological band structure of three-terminal graphene Josephson junctions. Using tunneling spectroscopy and magnetic flux gates, we performed a direct mapping of the Andreev bound state (ABS) energy spectrum as a function of two independent phase differences. This ABS spectrum exhibits the transition between gapped states associated with different topological invariants. Our results show the potential of graphene-based MTJJs for engineering band topologies in higher dimensions.