Andreev Reflections in NbN/Graphene Junctions under Large Magnetic Fields

Hybrid superconductor/graphene (SC/g) junctions are excellent candidates for investigating correlations between Cooper pairs and quantum Hall (QH) edge modes. Experimental studies challenging as Andreev reflections extremely sensitive to junction disorder high magnetic fields required form QH states. We fabricated low-resistance SC/g interfaces, composed of graphene contacted with NbN a barrier strength $Z\approx 0.4$, that remain superconducting under larger than $18$ T. establish the role graphene's Dirac band structure on zero-field demonstrate dynamic tunability reflection spectrum by moving boundary specular retro parallel fields. Through application perpendicular fields, we observe an oscillatory suppression 2-probe conductance in $\nu = 4$ Landau level attributed reduced efficiency processes at NbN/g interface, consistent theoretical predictions.