Andreev reflection and momentum filtering in quantum-wire/superconductive-graphene/quantum-wire junction
ABSTRACT Transport property of superconductive armchair graphene ribbon (AGR) connected to quantum-wire (QW) contacts is investigated via Landauer formalism combined with transfer matrix method. The scattering at the AGR/QW interface induces an obvious asymmetry in conductance as gate voltage varies. The transmission peak is located at momentum with a=0.142 nm. Andreev reflection (AR) enhances electronic transmission in the presence of hole reflection process. At lowest carrier density, the conductance of AGR in superconductive state becomes constant while the counterpart of semiconductive AGR in normal state decays exponentially with the length. The conductance increases with pair potential at low carrier density. The interplay between superconductivity and the scattering at the AGR/QW interface guides future application of superconductive graphene ribbon.
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ABSTRACT: Transport in disordered armchair graphene nanoribbons (AGR) with long-range correlation between quantum wire contacts is investigated by a transfer matrix combined with Landauer's formula. The metal-insulator transition is induced by disorder in neutral AGR. Therein, the conductance is one conductance quantum for the metallic phase and exponentially decays otherwise, when the length of AGR approaches infinity and far longer than its width. Similar to the case of long-range disorder, the conductance of neutral AGR first increases and then decreases while the conductance of doped AGR monotonically decreases, as the disorder strength increases. In the presence of strong disorder, the conductivity depends monotonically and non-monotonically on the aspect ratio for heavily doped and slightly doped AGR, respectively. For edge disordered graphene nanoribbon, the conductance increases with the disorder strength of long-range correlated disordered while no delocalization exists, since the edge disorder induces localization.Journal of Physics Condensed Matter 05/2012; 24(23):235303. · 2.22 Impact Factor
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ABSTRACT: Structural and electronic properties, including deformation, magnetic moment, Mulliken population, bond order, as well as electronic transport properties, of zigzag graphene nanoribbon (ZGNR) with Co adatoms on hollow sites are investigated by quasi-atomic minimal basis orbits (QUAMBOs), a first-principles tight binding (TB) scheme based on density functional theory (DFT), combined with a non-equilibrium Green's function. For electronic transport, below the Fermi level the transmission is strongly suppressed and spin dependent as a result of magnetism by Co adatom adsorption, while above the Fermi level the transmission is slightly distorted and spin independent. Due to the local environment dependence of QUAMBOs-TB parameters, we construct QUAMBOs-TB parameters of ZGNR leads and ZGNR with Co adatoms on hollow center sites by a divide-and-conquer approach, and accurately reproduce the electronic transmission behavior. Our QUAMBO-NEGF method is a new and promising way of examining electronic transport in large-scale systems.Journal of Physics Condensed Matter 03/2013; 25(10):105302. · 2.22 Impact Factor
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ABSTRACT: Our investigation of the transport properties in graphene nanoribbon's (GNR) between quantum wire contact and decoupled chains contact confirms general predictions for the transport through GNR for specific geometries. We found that electron-hole (e-h) symmetry depends sensitively on the contact and interface. For quantum wire contacts, the breaking of e-h symmetry occurs in armchair GNR due to odd-numbered ring at the interface, and at Dirac point the maximal transmission corresponds to the momentum k(y) = 2 pi/3 root 3a (a = 0.142 angstrom). The spatial density of states of armchair GNR is shown. Furthermore, the conductance at Dirac point is independent of contacts with dense modes.Chemical Physics Letters 11/2011; 516:225. · 1.99 Impact Factor