Mechanisms of Andreev reflection in graphene in a quantum Hall regime

We explore nonlocal Andreev signatures at the zeroth Landau level of quantum Hall (QH) graphene, considering effects of (i) disorder and (ii) Fermi energy mismatch between graphene and the superconductor (SC). In both cases, our calculations show the switching between normal and Andreev reflections, caused by intervalley scattering and transition to higher Landau levels at the QH/SC interface, respectively. While the first is suppressed with high-quality interfaces, the latter cannot be canceled with gate control and must be taken into account when analyzing measurements. Our results, despite in qualitative agreement with the data, contrast with the interpretation of a recent experimental work claiming the observation of chiral Andreev states interference [Nature Physics 16, (2020)], which we showed to be strongly sensitive to the interface orientation and, in general, unlikely to happen.