Andreev magneto-interferometry in topological hybrid junctions

We investigate the influence of the superconducting (S) proximity effect in the quantum Hall (QH) regime by computing the charge conductance flowing through a graphene-based QH/S/QH junction. This situation offers the exciting possibility of studying the fate of topological edge states when they experience tunneling processes through the superconductor. We predict the appearance of conductance peaks at integer values of the Landau level filling factor, as a consequence of the quantum interferences taking place at the junction, and provide a semiclassical analysis allowing for a natural interpretation of these interferences in terms of electron and hole trajectories propagating along the QH/S interfaces. Our results suggest that non-trivial junctions between topologically distinct phases could offer a highly tunable means of partitioning the flow of edge states.Comment: 5 pages, 3 figures; changed title and added discussion on topological junction

A metallic phase in quantum Hall systems

The electronic eigenstates of a quantum Hall (QH) system are chiral states. Strong inter-Landau-band mixings among these states can occur when the bandwidth is comparable to the spacing of two adjacent Landau bands. We show that mixing of localized states with opposite chirality can delocalize electronic states. Based on numerical results, we propose the existence of a metallic phase between two adjacent QH phases and between a QH phase and the insulating phase. This result is consistent with non-scaling behaviors observed in recent experiments on quantum-Hall-liquid-to-insulator transition.Comment: 5 pages, 3 figures. Will be published in Phys. Rev. Let