Andreev reflection and momentum filtering in quantum-wire/superconductive-graphene/quantum-wire junction

Ames Laboratory-US DOE, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, United States
Physics Letters A (Impact Factor: 1.63). 02/2011; DOI: 10.1016/j.physleta.2010.12.082

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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Study on the electronic transport of a large scale two dimensional system by the transfer matrix method (TMM) based on the Sch\"{o}rdinger equation suffers from the numerical instability. To address this problem, we propose a renormalized transfer matrix method (RTMM) by setting up a set of linear equations from U times of multiplication of traditional transfer matrix (U=N/S}with N and S being the atom number of length and the transfer step), and smaller S is required for wider systems. Then we solve the above linear equations by Gauss elimination method and further optimize to reduce the computational complexity from O(U^3M^3) to O(UM^3), in which M is the atom number of the width. Applying RTMM, we study transport properties of large scale pure and long-range correlated disordered armchair graphene nanoribbon (AGR) (carbon atoms up to 10^6 for pure case) between quantum wire contacts. As for pure AGR, the conductance is superlinear with the Fermi energy and the conductance is linear with the width while independent of the length, showing characteristics of ballistic transport. As for disordered AGR with long-range correlation, there is metal-insulator transition induced by the correlation strength of disorder. It is straightforward to extend RTMM to investigate transport in large scale system with irregular structure.
    Computer Physics Communications 05/2013; 185:856-861. DOI:10.1016/j.cpc.2013.12.006 · 2.41 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the transport properties through monolayer and bilayer graphene superlattices modulated by an in-plane homogeneous electric field based on the transfer matrix method. It is found that the angular range of the transmission probability through a graphene superlattice can be effectively controlled by the number of barriers and this results in the structure having efficient wavevector filters. As the number of barriers increases, this range shrinks. It is also shown that the conductance of the systems has an oscillatory behavior with respect to the barrier height and it decreases with the increasing number of barriers.
    Chinese Physics Letters 09/2013; 30(9):097201. DOI:10.1088/0256-307X/30/9/097201 · 0.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. DOI:10.1088/0953-8984/25/10/105302 · 2.22 Impact Factor