With its two degenerate valleys at the Fermi level, the band structure of graphene provides the opportunity to develop unconventional electronic applications. Herein, we show that electron and hole quasiparticles in graphene can be filtered according to which valley they occupy without the need to introduce confinement. The proposed valley filter is based on scattering off a recently observed line defect in graphene. Quantum transport calculations show that the line defect is semitransparent and that quasiparticles arriving at the line defect with a high angle of incidence are transmitted with a valley polarization near 100%.

Stimulated by recent advances in isolating graphene and similarities to single-wall carbon nanotubes, simulations were performed to assess the effects of static disorder on the conductance of metallic armchair- and zigzag-edge graphene nanostrips. Both strip types were found to have outstanding ballistic transport properties in the presence of a substrate-induced disorder. However, only the zigzag-edge strips retain these properties in the presence of irregular edges, making them better initial synthetic targets for ballistic device applications.

Submitted for the MAR13 Meeting of The American Physical Society Valley polarization and intervalley scattering in monolayer MoS 2 G. KIOSEOGLOU, University of Crete, A.T. HANBICKI, M. CURRIE, A.L. FRIEDMAN, D. GUNLYCKE, B.T. JONKER, Naval Research Lab-Single layer MoS 2 is a prime candidate material for implementing valleytronics because minima in the bandstructure at inequivalent K points of the Brillouin zone can be independently populated, thus making the valley index a potential state variable for information processing. Light of a particular helicity populates only one of the two K-valleys (either K or K') resulting in a strong emission at around 1.9 eV associated with a direct transition. We use energy and helicity dependent optical pumping to analyze the coupling of the valley and spin indices to the depolarization of emitted light. The circular polarization of the photoluminescence is very high for photoexcitation near the bandgap, and has a power-law decrease as the photo-excitation energy increases. We identify phonon-assisted intervalley scattering as the primary spin relaxation mechanism and present a model of depolarization that explains the wide variation in values for the optical polarization reported in the literature. Our results elucidate the basic processes that control the unique properties of this material and should help to realize future valleytronic applications. This work was supported by core programs at NRL and the NRL Nanoscience Institute.

We investigate the entanglement arising naturally in a 1D Ising chain in a magnetic field in an arbitrary direction. We find that for different temperatures, different orientations of the magnetic field give maximum entanglement. In the high temperature limit, this optimal orientation corresponds to the magnetic field being perpendicular to the Ising orientation (z direction). In the low temperature limit, we find that varying the angle of the magnetic field very slightly from the z direction leads to a rapid rise in entanglement. We also find that the orientation of the magnetic field for maximum entanglement varies with the field amplitude. Furthermore, we have derived a simple rule for the mixing of concurrences (a measure of entanglement) due to mixing of pure states satisfying certain conditions.