L. Brey

Vacancy-induced magnetism in graphene and graphene ribbons

This work was financially supported by MEC-Spain under Grant Nos. MAT2007-65487, MAT2006-03741, and CONSOLIDER CSD2007-00010, and by Generalitat Valenciana under Grant No. ACOMP07/054.

Edge states and the quantized Hall effect in graphene

We study edges states of graphene ribbons in the quantized Hall regime, and show that they can be described within a continuum model (the Dirac equation) when appropriate boundary conditions are adopted. The two simplest terminations, zigzag and armchair edges, are studied in detail. For zigzag edges, we find that the lowest Landau level states terminate in two types of edge states, dispersionless and current-carrying surface states. The latter involve components on different sublattices that may be separated by distances far greater than the magnetic length. For armchair edges, the boundary conditions are met by admixing states from different valleys, and we show that this leads to a single set of edges states for the lowest Landau level and two sets for all higher Landau levels. In both cases, the resulting Hall conductance step for the lowest Landau level is half that between higher Landau levels, as observed in experiment.

Diluted graphene antiferromagnet.

We study RKKY interactions between local magnetic moments for both doped and undoped graphene. In the former case interactions for moments located on definite sublattices fall off as 1/R2, whereas for those placed at interstitial sites they decay as 1/R3. The interactions are primarily (anti)ferromagnetic for moments on (opposite) equivalent sublattices, suggesting that at low temperature dilute magnetic moments embedded in graphene can order into a state analogous to that of a dilute antiferromagnet. In the undoped case we find no net magnetic moment in the ground state, and demonstrate numerically this effect for ribbons, suggesting the possibility of an unusual spin-transfer device.

Surface electronic structure and magnetic properties of doped manganites

The electronic structure and magnetic properties of doped manganites surfaces are investigated. It is assumed that, at the outermost layer, the environment of the Mn ions does not have cubic symmetry. The

CARBON NANOELECTRONICS: UNZIPPING TUBES INTO GRAPHENE RIBBONS

{e}_{g}

Skyrme Crystal in a Two-Dimensional Electron Gas

orbitals are split and the double exchange mechanism is weakened. The charge state of the Mn ions is modified, and the magnetic ordering of the spins tends to be antiferromagnetic. The surface magnetization and the dependence of the transport properties through the resulting surface barrier on applied magnetic field and temperature is analyzed.

Electronic transport through bilayer graphene flakes

We report on the transport properties of novel carbon nanostructures made of partially unzipped carbon nanotubes, which can be regarded as a seamless junction of a tube and a nanoribbon. We find that graphene nanoribbons act at certain energy ranges as perfect valley filters for carbon nanotubes, with the maximum possible conductance. Our results show that a partially unzipped carbon nanotube is a magnetoresistive device, with a very large value of magnetoresistance. We explore the properties of several structures combining nanotubes and graphene nanoribbons, demonstrating that they behave as optimal contacts for each other, and opening a new route for the design of mixed graphene-nanotube devices.

Excitations from Filled Landau Levels in Graphene

The ground state of a two-dimensional electron gas at Landau level filling factors near

Collective Excitations, NMR, and Phase Transitions in Skyrme Crystals

\nu =1

Electronic structure of gated graphene and graphene ribbons

is a Skyrme crystal with long range order in the positions and orientations of the topologically and electrically charged elementary excitations of the