Andreev reflection (AR) is the underlying phenomena that determine the quasiparticle dynamics at the junction of a superconductor with any non-superconducting material, which in turn determine the transport properties of the junction. In conventional normal metal – superconductor (NS) junctions the AR is always retro type. We have carried out the transport measurements at the Van der Waals interface of single layer graphene and NbSe2 superconductor, which reveal the transition from retro to a non-retro type AR dominated transport near the Dirac point. The physics of AR is predicted to be intriguingly different in quantum Hall (QH) regime. We observed signature of AR at the junction of the QH state in graphene and the NbSe2 superconductor. A completely new kind of AR, named as inter-Landau-level AR, is observed when Fermi energy is tuned near the charge neutrality point. Further, when the Fermi energy is tuned between Landau levels an edge state is formed at the QH – superconductor interface, which contains an equal mixture of electron and hole due to repetitive AR; such a state is called an Andreev edge state (AES). Because of this unique electron hole mixing process shot noise is generated in a QH – superconductor junction, which carries the information of quasiparticle charge of the superconductor. We performed both conductance and shot noise measurements in a graphene QH connected to type-II superconductor MoRe and extracted the exact ‘2e’ charge of quasiparticle in a superconductor. In doing so, we realize a unique transition from non-interacting hot electron to interacting hot electron regime of the AES with increasing magnetic field.

1) Andreev reflection near the Dirac point at the graphene‐ NbSe2 junction, MR Sahu et al., Physical Review B 94 (23), 235451.

2) Inter‐Landau‐level Andreev Reflection at the Dirac Point in a Graphene Quantum Hall State Coupled to a NbSe2 Superconductor, MR Sahu et al., Physical review letters 121 (8), 086809.

3) 2e charge transport in a quantum Hall‐superconductor junction revealed by shot noise. MR Sahu et al., unpublished.