M. P. López-Sancho

Local defects and ferromagnetism in graphene layers

We study the changes in the electronic structure induced by lattice defects in graphene planes. In many cases, lattice distortions give rise to localized states at the Fermi level. Electron-electron interactions lead to the existence of local moments. The RKKY interaction between these moments is always ferromagnetic, due to the semimetallic properties of graphene.

Magnetic moments in the presence of topological defects in graphene

Instituto de Ciencia de Materiales de Madrid,CSIC, Cantoblanco, E-28049 Madrid, Spain.(Dated: June 21, 2008)We study the influence of pentagons, dislocations and other topological defects breaking thesublattice symmetry on the magnetic properties of a graphene lattice in a Hartree Fock mean fieldscheme. The ground state of the system with a number of vacancies or similar defects belonging tothe same sublattice is known to have total spin equal to the number of uncoordinated atoms in thelattice for any value of the Coulomb repulsion U according to the Lieb theorem. We show that thepresence of a single pentagonal ring in a large lattice is enough to alter this behavior and a criticalvalue of U is needed to get the polarized ground state. Glide dislocations made of a pentagon-heptagon pair induce more dramatic changes on the lattice and the critical value of U needed topolarize the ground state depends on the density and on the relative position of the defects. Wefound a region in parameter space where the polarized and unpolarized ground states coexist.

New Type of Vacancy-Induced Localized States in Multilayer Graphene

We demonstrate the existence of a new type of zero energy state associated with vacancies in multilayer graphene that has a finite amplitude over the layer with a vacancy and adjacent layers, and the peculiarity of being quasilocalized in the former and totally delocalized in the adjacent ones. In a bilayer, when a gap is induced in the system by applying a perpendicular electric field, these states become truly localized with a normalizable wave function. A transition from a localized to an extended state can be tuned by the external gate for experimentally accessible values of parameters.

Effect of electron-electron interaction on the Fermi surface topology of doped graphene

The electron-electron interactions effects on the shape of the Fermi surface of doped graphene are investigated. The actual discrete nature of the lattice is fully taken into account. A

Curvature-induced anisotropic spin-orbit splitting in carbon nanotubes

\ensuremath{\pi}

Momentum dependence of spin–orbit interaction effects in single-layer and multi-layer transition metal dichalcogenides

-band tight-binding model, with nearest-neighbor hopping integrals, is considered. We calculate the self-energy corrections at zero temperature. Long and short-range Coulomb interactions are included. The exchange self-energy corrections for graphene preserve the trigonal warping of the Fermi surface topology, although rounding the triangular shape. The band velocity is renormalized to higher value. Corrections induced by a local Coulomb interaction, calculated by second-order perturbation theory, do deform anisotropically the Fermi surface shape. Results are compared to experimental observations and to other theoretical results.

Temperature dependence of the dielectric constant and resistivity of diluted magnetic semiconductors

We have theoretically explored the spin-orbit interaction in carbon nanotubes. We show that, besides the dependences on chirality and diameter, the effects of spin-orbit coupling are anisotropic: spin-orbit splitting is larger for the higher valence or the lower electron band depending on the specific tube. Different tube behaviors can be grouped in three families, according to the so-called chiral index. Curvature-induced changes in the orbital hybridization have a crucial role, and they are shown to be family dependent. Our results explain recent experimental results which have evidenced the importance of spin-orbit effects in carbon nanotubes.

Confinement of electrons in layered metals.

One of the main characteristics of the new family of two-dimensional crystals of semiconducting transition metal dichalcogenides (TMDs) is the strong spin–orbit interaction, which makes them very promising for future applications in spintronics and valleytronics devices. Here we present a detailed study of the effect of spin–orbit coupling (SOC) on the band structure of single-layer and bulk TMDs, including explicitly the role of the chalcogen orbitals and their hybridization with the transition metal atoms. To this aim, we combine density functional theory (DFT) calculations with a Slater–Koster tight-binding (TB) model. Whereas most of the previous TB models have been restricted to the K and K’ points of the Brillouin zone (BZ), here we consider the effect of SOC in the whole BZ, and the results are compared to the band structure obtained by DFT methods. The TB model is used to analyze the effect of SOC in the band structure, considering separately the contributions from the transition metal and the chalcogen atoms. Finally, we present a scenario where, in the case of strong SOC, the spin/orbital/valley entanglement at the minimum of the conduction band at Q can be probed and be of experimental interest in the most common cases of electron-doping reported for this family of compounds.

Effect of pressure on the magnetism of bilayer graphene

We study the effect that the ferromagnetic order has on the electrical properties of diluted magnetic semiconductors. We analyze the temperature dependence of the dielectric constant and of the resistivity of

Pinning and switching of magnetic moments in bilayer graphene

{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}.