[{"type":"speech","title":"Charge transport in disordered superconductor-graphene junctions","issued":{"date-parts":[["2010"]]},"author":[{"family":"Metalidis","given":"G."},{"family":"Golubev","given":"D."},{"family":"Sch\u00f6n","given":"G."}],"note":"Fr\u00fchjahrstagung DPG, Fachverband Halbleiterphysik, Regensburg, 21.-26.M\u00e4rz 2010 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.45(2010) HL 7.10 Fr\u00fchjahrstagung DPG, Fachverband Tiefe Temperaturen, Regensburg, 21.-26.M\u00e4rz 2010 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.45(2010) TT 1.10","abstract":"Semiconductor Physics Division (HL)\nMonday\n\u2014 2 Instituto de Ciencia de Materiales de Madrid, Spain\nWe analyze the single particle states at the edges of graphene quantum dots of arbitrary shapes. By combining analytical and numerical\narguments, we show that localized edge states, distinct from extended\nones, exist in dots of all dimensions. The number of these states is\nproportional to the circumference of the dot measured in lattice constants. Perturbations breaking electron-hole symmetry shift the edge\nstates away from zero energy but do not change their total amount.\nRecent theoretical [1] and experimental [2] works have shown that\nspin-orbit couplings in graphene can play a relevant role. Motivated\nby these results, we address the problem of spin transport in graphene\nthrough spin-orbit nanostructures, i.e. regions of inhomogeneous spinorbit coupling on the nanometer scale. In analogy with the case of\nusual two-dimensional electron gases, we discuss the phenomenon of\nspin-double refraction [3,4] and its consequences on the spin polarization. In particular we study the transmission properties of a singleand a double-interface between a normal region and a region with finite\nspin-orbit coupling, and analyze the polarization properties of these\nsystems. In addition, for the case of the single interface, we consider\nthe formation of bound states localized at the interface, analogous to\nthe states occuring at the edges of graphene in the weak topological\ninsulator regime discussed by Kane and Mele [5].\n[1] D. Huertas-Hernando, et al., Phys. Rev. Lett. 103, 146801 (2009).\n[2] A. Varykhalov, et al., Phys. Rev. Lett. 101, 157601 (2008).\n[3] V. M. Ramaglia, et al., Eur. Phys. J. B 36, 365 (2003).\n[4] V. M. Ramaglia, et al., J. Phys.: Condens. Matter 16, 9143 (2004).\n[5] C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 226801 (2005).\n15 min. break\nHL 7.6\nMon 11:45\nH18\nGraphene: Relativistic transport in a nearly perfect quantum\nliquid \u2014 \u2219Lars Fritz1 , Markus Mueller2 , Joerg Schmalian3 ,\nSalam International Centre for Theoretical Physics, Strada Costiera\n11, 34151 Trieste, Italy \u2014 3 Department of Physics and Astronomy\nIowa State University Ames, Iowa 50011, USA \u2014 4 Harvard University, 17 Oxford Street, Cambridge, MA 02138, USA\nElectrons and holes in clean, charge-neutral graphene behave like a\nstrongly coupled relativistic liquid. The thermo-electric transport\nproperties of the interacting Dirac quasiparticles are rather special, being constrained by an emergent Lorentz covariance at hydrodynamic\nfrequency scales. At small carrier density and high temperatures,\ngraphene exhibits signatures of a quantum critical system with an inelastic scattering rate set only by temperature, a conductivity with a\nnearly universal value, solely due to electron-hole friction, and a very\nlow viscosity. In this regime one finds pronounced deviations from\nstandard Fermi liquid behavior. These results, obtained by Boltzmann transport theory at weak electron-electron coupling, are fully\nconsistent with the predictions of relativistic hydrodynamics.\nHL 7.7\nMon 12:00\nH18\nHyperfine interaction and electron-spin decoherence\nin graphene and carbon nanotube quantum dots \u2014\n\u2219Jan Fischer1 , Bjoern Trauzettel2 , and Daniel Loss1 \u2014\n1 Department of Physics, University of Basel, Klingelbergstrasse 82,\n4056 Basel, Switzerland \u2014 2 Institute of Theoretical Physics and Astrophysics, University of W\u00fcrzburg, D-97074 W\u00fcrzburg, Germany\nWe analytically calculate the nuclear-spin interactions of a single electron confined to a carbon nanotube or graphene quantum dot [1].\nWhile the conduction-band states in graphene are p-type, the accordant states in a carbon nanotube are sp-hybridized due to curvature.\nThis leads to an interesting interplay between isotropic and anisotropic\nhyperfine interactions. By using only analytical methods, we are able\nto show how the interaction strength depends on important physical parameters, such as curvature and isotope abundances. We show\nthat for the investigated carbon structures, the 13 C hyperfine coupling\nstrength is less than 1 \ud835\udf07eV, and that the associated electron-spin decoherence time can be expected to be several tens of microseconds or\nlonger, depending on the abundance of spin-carrying 13 C nuclei. Furthermore, we find that the hyperfine-induced Knight shift is highly\nanisotropic, both in graphene and in nanotubes of arbitrary chirality.\n(2009)\nHL 7.8\nMon 12:15\nH18\nSpin transport in graphene with inhomogeneous spin-orbit\ncoupling \u2014 \u2219Dario Bercioux1 and Alessandro De Martino2 \u2014\nHL 7.9\nMon 12:30\nH18\nEdge effects in quantum transport and quasiparticle spectra of graphene nanostructures \u2014 \u2219J\u00fcrgen Wurm1,2 , Klaus\nPhysik, Universit\u00e4t Regensburg, 93040 Regensburg \u2014 2 Faculty of Engineering and Natural Sciences, Sabanc\u0131 University, Orhanl\u0131 - Tuzla,\n34956, Turkey\nIn this work, we focus on the spectral and transport properties of\ngraphene nanostructures. In recent work, we studied the effects of\nedges on the transport and spectral properties of graphene quantum\ndots, as well as on the conductance of graphene nanoribbons numerically [1,2]. Some edges can lead to effective time reversal symmetry\nbreaking, others are effective intervalley scatterers. In this work, we\ndevelop a theory that is capable of handling such effects in graphene\nnanostructures. We do this in two steps. First, we derive an exact expression for the Green function of a graphene flake, where each term in\nthis expansion corresponds to the specific number of times the quasiparticle hits the edge. Second, we use the Green function to calculate:\n(i) the spectra for closed systems and (ii) the conductance of open\nsystems. In particular, we focus on phase coherent effects, such as\nthe weak localization correction to the average conductance, and the\nuniversal conductance fluctuations. Moreover, we show how the size\nof these effects depends on the edges.\n[1] J. Wurm et al., Phys. Rev. Lett. 102, 056806 (2009)\n[2] J. Wurm et al., New J. Phys. 11, 095022 (2009)\nHL 7.10\nMon 12:45\nH18\njunctions \u2014 \u2219Georgo Metalidis1 , Dmitry Golubev2 , and Gerd\nWe consider the charge transport through superconductor-graphene\ntunnel junctions, including the effect of disorder. Coherent scattering\non elastic impurities in the graphene layer can give rise to multiple\nreflections at the graphene-superconductor interface, and can thereby\nincrease the probability of Andreev reflection, leading to an enhancement of the subgap conductance above its classical value. Although\nthe phenomenon is known already from heterostructures involving normal metals, we have studied how graphenes peculiar dispersion relation\ninfluences the effect.\nHL 8: Organic Electronics and Photovoltaics I (Joint Session with DS\/CPP\/O)\nTime: Monday 10:15\u201312:30\nLocation: H8\nHL 8.1\nMon 10:15\nH8\nIn recent years the interest in ambipolar organic light-emitting field-\neffect transistors has increased steadily as the devices combine switching behaviour of transistors with light emission. Usually, small\nmolecules and polymers with a band gap in the visible spectral range\nserve as semiconducting ma","kit-publication-id":"230080400"}]