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We discuss the low-energy electronic states and transport properties of graphene nanoribbons. In zigzag nanoribbons with long-ranged impurities, a single perfectly conducting channel emerges associated with such a chiral mode due to edge states, i.e. the absence of the localization. In armchair nanoribbons, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wavefunction. Our numerical simulations reveal the unusual electronic transport properties of graphene nanoribbons as quantum wires. [ABSTRACT FROM AUTHOR]

We have investigated charge and spin gap properties of zigzag edge graphene nanoribbons (ZGNRs) modeled within Hubbard Hamiltonian with onsite electron-electron interaction using semi-empirical many-body configuration interaction (CI) method. The charge gap behavior resembles the mean-field results, showing minima near Dirac point. We have observed unprecedented gap-less spin excitations over the flat band region. Moreover, doping the ZGNRs with holes reduces both the charge and spin gaps, inducing metallic and magnetic behavior, which can be exploited to fabricate spintronic devices. [ABSTRACT FROM AUTHOR]

The low-energy band structure of graphene ribbons with zigzag edges have two valleys well separated in momentum space, related to the two Dirac points of the graphene spectrum. The propagating modes in each valley contain a single chiral mode originating from a partially flat band at band center. This feature gives rise to a perfectly conducting channel in the disordered system, if the impurity scattering does not connect the two valleys, i.e. for long-range impurity potentials. Ribbons with short-range impurity potentials, however, through inter-valley scattering display ordinary localization behavior. [ABSTRACT FROM AUTHOR]

The ferromagnetic system with orbital hybridization and onsite spin-orbit coupling shows finite anomalous and spin Hall conductivity. In this paper, we study the edge effect on charge and spin transport properties in quasi-one dimensional anomalous Hall system. It is found that the existence of the intriguing spontaneous edge spin current which flows even in the absence of the internal magnetic field, unless either orbital hybridization hopping or spin-orbit interaction is turned off. The origin of the surface spin current is the consequence of the quantum interference effect between parity violation due to the orbital hybridization and spin-orbit interaction. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The properties of quantum electron transport in disordered wires with symplectic symmetry is studied by a random-matrix approach and a numerical simulation. It has been shown that the behavior of the conductance crucially depends on whether the number of conducting channels is even or odd. We focus on the long-wire regime where the wire length is much longer than the conductance decay length, and evaluate the averaged conductance for the even- and odd-channel cases. From the random-matrix theory, we find that the dimensionless conductance in the even-channel case decays exponentially as → 0 with increasing system length, while → 1 in the odd-channel case. It is also shown that the decay of godd is much faster than geven. We examine this even- odd difference by a numerical simulation based on the tight-binding model. The numerical results are in good agreement with the random-matrix results. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]