▎ 摘　　要

Ongoing experimental progress in the preparation of ultraclean graphene/superconductor ( SC) interfaces enabled the recent observation of specular interband Andreev reflections ( ARs) at bilayer graphene ( BLG)/NbSe2 van der Waals interfaces [ Efetov et al., Nat. Phys. 12, 328 ( 2016)]. Motivated by this experiment we theoretically study the differential conductance across a BLG/SC interface at the continuous transition from high to ultralow Fermi energies EF in BLG. Using the Bogoliubov-de Gennes equations and the Blonder-Tinkham-Klapwijk formalism we derive analytical expressions for the differential conductance across the BLG/SC interface. We find a characteristic signature of the crossover from intraband retro ( high EF) to interband specular ( low EF) ARs that manifests itself in a strongly suppressed interfacial conductance when the excitation energy vertical bar epsilon vertical bar = vertical bar E-F vertical bar < Delta ( the SC gap). The sharpness of these conductance dips is strongly dependent on the size of the potential step at the BLG/SC interface U-0.