Emergence of superlattice Dirac points in graphene on hexagonal boron nitride

Abstract

It is well known that graphene deposited on hexagonal boron nitride produces moiré patterns in scanning tunnelling microscopy images. The interaction that produces this pattern also produces a commensurate periodic potential that generates a set of Dirac points that are different from those of the graphene lattice itself. The Schrödinger equation dictates that the propagation of nearly free electrons through a weak periodic potential results in the opening of bandgaps near points of the reciprocal lattice known as Brillouin zone boundaries1. However, in the case of massless Dirac fermions, it has been predicted that the chirality of the charge carriers prevents the opening of a bandgap and instead new Dirac points appear in the electronic structure of the material2,3. Graphene on hexagonal boron nitride exhibits a rotation-dependent moiré pattern4,5. Here, we show experimentally and theoretically that this moiré pattern acts as a weak periodic potential and thereby leads to the emergence of a new set of Dirac points at an energy determined by its wavelength. The new massless Dirac fermions generated at these superlattice Dirac points are characterized by a significantly reduced Fermi velocity. Furthermore, the local density of states near these Dirac cones exhibits hexagonal modulation due to the influence of the periodic potential.