Tunable single particle and many body physics in graphene

Abstract

This thesis studies how the rudimentary attributes of graphene's charge carriers, and local moments on its surface, can be directly manipulated and controlled with electrostatic potentials. We first consider bilayer graphene subject to a spatially varying electrostatic potential that forms two neighbouring regions with opposite interlayer bias. Along the boundary, 1D chiral "kink" states emerge. We find that these 1D modes behave as a strongly interacting Luttinger liquid whose properties can be tuned via an external gate. Next, we consider superlattices in bilayer graphene. Superlattices are seen to have a more dramatic effect on bilayer graphene than monolayer graphene because the quasi-particles are changed in a fundamental way; the dispersion goes from a quadratic band touching point to linearly dispersing Dirac cones. We illustrate that a 1D superlattice of either the chemical potential or an interlayer bias generates multiple anisotropic Dirac cones. General arguments delineate how certain symmetries protect the Dirac points. We then map the Hamiltonian of an interlayer bias superlattice onto a chain model comprised of "topological" modes. This is followed by another study that considers the effect of a magnetic field on graphene superlattices. We show that magnetotransport measurements in a weak perpendicular magnetic field probe the number of emergent Dirac points and reveal details about the dispersion. In the case of bilayer graphene, we also discuss the properties of kink states in an applied magnetic field. Finally, we investigate local moment formation of adatoms on bilayer graphene using an Anderson impurity model. We identify regions where the local moments can be turned on or off by applying a external electric fields. In addition, we compute the RKKY interaction between local moments and show how it too can be controlled with electric fields.