Klein tunneling and cone transport in AA-stacked bilayer graphene

We investigate the quantum tunneling of electrons in an AA-stacked bilayer graphene (BLG) n-p junction and n-p-n junction. We show that Klein tunneling of an electron can occur in this system. The quasiparticles are not only chiral but are additionally described by a "cone index." Due to the orthogonality of states with different cone indexes, electron transport across a potential barrier must strictly conserve the cone index, and this leads to the protected cone transport which is unique in AA-stacked BLG. Together with the negative refraction of electrons, electrons residing in different cones can be spatially separated according to their cone index when transmitted across an n-p junction. This suggests the possibility of "cone-tronic" devices based on AA-stacked BLG. Finally, we calculate the junction conductance of the system.