CPM Seminar

Transport and interaction effects in moire patterns formed by graphene on boron nitride

Ashley DaSilva

University of Texas

Graphene and boron nitride (BN) both have honeycomb lattices, but with slightly different lattice constants. Because of the low defect density and atomic flatness of BN substrates, they are often used as high-quality substrates for graphene devices. When graphene is placed on BN with an arbitrary relative orientation, the interaction between graphene electrons and the substrate is weak. However, when the graphene and BN lattices are aligned or nearly aligned, the small difference between the two hexagonal lattice leads to the formation of a long period moire pattern in all local electronic observables. The interaction between graphene electrons and the BN substrate is due to both the interaction of electrons with the BN lattice and the structural relaxation of carbon atoms in the graphene lattice. It changes the electronic structure of graphene, causing a gap to open at the Dirac point and secondary band crossings to appear at higher energy. I will describe a continuum model of the graphene substrate interaction that is based on first principles electronic structure calculations and use it to evaluate the gap at the primary Dirac point which agrees with experiment when electron-electron interactions are included. The secondary gaps are located at the Fermi level when the graphene sheet has four carriers per moire unit cell and lead to transport and far-infrared absorption features that are remarkably particle-hole asymmetric. The particle-hole asymmetry can be explained as a consequence of interference between honeycomb-sublattice-dependent potential and inter-sublattice hopping contributions to the substrate interaction Hamiltonian.