Complete light absorption in graphene-metamaterial corrugated structures

We show that surface-plasmon polaritons excited in negative permittivity metamaterials having shallow periodic surface corrugation profiles can be explored to push the absorption of single and continuous sheets of graphene up to 100%. In the relaxation regime, the position of the plasmonic resonances of the hybrid system is determined by the plasma frequency of the metamaterial, allowing the frequency range for enhanced absorption to be set without the need of engineering graphene.Comment: 6 pages, 4 figures; published version: text revised and references adde

Weak ferromagnetism and spiral spin structures in honeycomb Hubbard planes

Within the Hartree Fock- RPA analysis, we derive the spin wave spectrum for the weak ferromagnetic phase of the Hubbard model on the honeycomb lattice. Assuming a uniform magnetization, the polar (optical) and acoustic branches of the spin wave excitations are determined. The bipartite lattice geometry produces a q-dependent phase difference between the spin wave amplitudes on the two sub-lattices. We also find an instability of the uniform weakly magnetized configuration to a weak antiferromagnetic spiraling spin structure, in the lattice plane, with wave vector Q along the Gamma-K direction, for electron densities n>0.6. We discuss the effect of diagonal disorder on both the creation of electron bound states, enhancement of the density of states, and the possible relevance of these effects to disorder induced ferromagnetism, as observed in proton irradiated graphite.Comment: 13 pages, 7 figure

Confined magneto-optical waves in graphene

The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tuneable, by changing the magnetic field or the Fermi energy.Comment: 9 pages, 7 figures. published version: text and figures revised and updated + new references and one figure adde

Wigner's little group and Berry's phase for massless particles

The ``little group'' for massless particles (namely, the Lorentz transformations $\Lambda$ that leave a null vector invariant) is isomorphic to the Euclidean group E2: translations and rotations in a plane. We show how to obtain explicitly the rotation angle of E2 as a function of $\Lambda$ and we relate that angle to Berry's topological phase. Some particles admit both signs of helicity, and it is then possible to define a reduced density matrix for their polarization. However, that density matrix is physically meaningless, because it has no transformation law under the Lorentz group, even under ordinary rotations.Comment: 4 pages revte

Algebraic solution of a graphene layer in a transverse electric and perpendicular magnetic fields

We present an exact algebraic solution of a single graphene plane in transverse electric and perpendicular magnetic fields. The method presented gives both the eigen-values and the eigen-functions of the graphene plane. It is shown that the eigen-states of the problem can be casted in terms of coherent states, which appears in a natural way from the formalism.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics Condensed Matte

Magnetic and superconducting instabilities in the periodic Anderson model: an RPA stud

We study the magnetic and superconducting instabilities of the periodic Anderson model with infinite Coulomb repulsion U in the random phase approximation. The Neel temperature and the superconducting critical temperature are obtained as functions of electronic density (chemical pressure) and hybridization V (pressure). It is found that close to the region where the system exhibits magnetic order the critical temperature T_c is much smaller than the Neel temperature, in qualitative agreement with some T_N/T_c ratios found for some heavy-fermion materials. In our study, all the magnetic and superconducting physical behaviour of the system has its origin in the fluctuating boson fields implementing the infinite on-site Coulomb repulsion among the f-electrons.Comment: 9 pages, 2 figure