Valley-momentum locking in a graphene superlattice with Y-shaped Kekulé bond texture

Official URL: http://dx.doi.org/10.1088/1367-2630/aaa7e5

Recent experiments by Gutierrez et al (2016 Nat. Phys. 12 950) on a graphene-copper superlattice have revealed an unusual Kekule bond texture in the honeycomb lattice-a Y-shaped modulation of weak and strong bonds with a wave vector connecting two Dirac points. We show that this so-called 'Kek-Y' texture produces two species of massless Dirac fermions, with valley isospin locked parallel or antiparallel to the direction of motion. In a magnetic field B, the valley degeneracy of the B-dependent Landau levels is removed by the valley-momentum locking but a B-independent and valley-degenerate zero-mode remains.