📝 SummarXiv

Abstract

We theoretically study the Andreev reflection (AR) in AA-stacked bilayer graphene/superconductor (AABG/SC) junction. AABG has a linear gapless energy band with two shifted Dirac cones and the electronic states are described by the cone indices. The results indicate that the property of AR strongly depends on the cone degree of freedom. In the absence of the inter-layer potential difference, only intra-cone AR and normal reflection (NR) could occur, and the inter-cone process is forbidden. By adjusting the potential, the intra-cone AR can be specular AR (SAR) in one cone and it is retro-AR (RAR) in the other cone. The existence of the inter-layer potential difference would lead to the inter-cone scattering. As a result, double ARs and double NRs can take place between the two cones. The inter-cone SAR could happen in a broad potential region. Furthermore, the inter-cone retro-NR (RNR) could happen as well. The switch between SAR and RAR, and the switch between specular NR (SNR) and RNR can be achieved by regulating the potential. Therefore, different cone carriers can be separated spatially based on the RAR and SAR. The cone-dependent Andreev conductance may be separately measured near the critical values where RAR crosses over to SAR.