Signatures of evanescent transport in ballistic suspended graphene-superconductor junctions

摘要: In Dirac materials, the low energy excitations behave like ultra-relativistic massless particles with linear dispersion. A particularly intriguing phenomenon arises intrinsic charge transport behavior at point where density approaches zero. graphene, a 2-D fermion gas system, it was predicted that near is carried by evanescent modes, resulting in unconventional “pseudo-diffusive” even absence of disorder. past decade, experimental observation this remained challenging due to presence strong disorder graphene devices which limits accessibility carrier regime close enough point. Here we report measurements on ballistic suspended graphene-Niobium Josephson weak links demonstrate transition from pseudo-diffusive below ~1010 cm−2. Approaching point, sub-harmonic gap structures multiple Andreev reflections display Fermi energy-dependence and become increasingly pronounced, while normalized excess current through superconductor-graphene interface decreases sharply. Our observations are qualitative agreement long standing theoretical prediction for emergence mediated graphene.