Crossed Andreev reflection in the fractional quantum Hall state of graphene*

We construct high-quality graphene-based van der Waals devices with narrow superconducting niobium nitride (NbN) electrodes, in which superconductivity and robust fqH can coexist. We find crossed Andreev reflection (CAR) across the superconductor separating two qH edges. In integer fillings, we find a filling-independent CAR probability robust to changes in magnetic field and temperature, which we attribute to spin-orbit coupling in NbN allowing for Andreev reflection between spin-polarized edges. Interestingly, while CAR in the hole-conjugate fractions has similar behavior, CAR probabilities in the particle-like fractional fillings are markedly higher and depend strongly on temperature and magnetic field. We investigate this behavior by tuning the doping of the NbN interface while keeping bulk filling constant. These results provide a route to realize novel topological superconducting phases in fqH–superconductor hybrid devices based on graphene and NbN.