1,721,061 research outputs found
Analytic and numeric Green's functions for a two-dimensional electron gas in an orthogonal magnetic field
No full textWe have derived closed analytic expressions for the Green’s function of an electron in a two-dimensional electron gas threaded by a uniform perpendicular magnetic field, also in the presence of a uniform electric field and of a parabolic spatial confinement. A workable and powerful numerical procedure for the calculation of the Green’s functions for a large infinitely extended quantum wire is considered exploiting a lattice model for the wire, the tight-binding representation for the corresponding matrix Green’s function, and the Peierls phase factor in the Hamiltonian hopping matrix element to account for the magnetic field. The numerical evaluation of the Green’s function has been performed by means of the decimation–renormalization method, and quite satisfactorily compared with the analytic results worked out in this paper. As an example of the versatility of the numerical and analytic tools here presented, the peculiar semilocal character of the magnetic Green’s function is studied in detail because of its basic importance in determining magneto-transport properties in mesoscopic systems
Conductance distributions at the metal-insulator crossover in quasi 1-D pseudorandom wires
No full textA study of the distribution of conductances, P(g), for quasi-one-dimensional (multichain) pseudorandom systems is here presented. We focus on the crossover between the metallic and the insulating regimes with reference to the case of "cosine" and "tangent" pseudorandom potentials. The results are compared with those obtained for the truly random disordered systems with the same geometry. A rich variety of shapes of P(g) is thus evidenced in the crossover-transport regime and, in the case of identical interacting chains composing the device, we have shown that the conductance distribution of the system can be obtained from the results for the single pseudorandom chain
Field-effect resistance of gated graphitic polymeric ribbons: Numerical simulations
No full textWe investigate the electronic and transport properties of undistorted gated polymers of the polyacene family by exploiting the tight-binding model for the system Hamiltonian and the nonequilibrium Keldysh formalism for charge transport. Our simulations reveal that, for smooth gate potentials varying only along the ribbon longitudinal axis, the electronic conductance as a function of the energy is quantized and presents crossover from conducting to insulating regimes. We interpret this behavior on the basis of the band structures entailed by the bipartite honeycomb topology of the lattice and the symmetry of the ribbons with even or odd number of chains (even-odd effect)
Scattering of chiral currents by quantum point contacts
No full textThe conductive channels and the current distributions through a narrow quantum point contact (QPC) in a two-dimensional electron gas threaded by a uniform magnetic field are studied using the Keldysh nonequilibrium Green's function formalism and a site representation of the electron Hamiltonian. We show that when the conditions of chiral transport regime are met in the two regions separated by the QPC, exact quantization in integer multiples of 2e2/h is maintained both for the conductance of the incident current and the backscattered plus transmitted currents
Current profiles and semilocal Green's functions in quantum magnetotransport
No full textThe study of current profiles in the two-dimensional electron gas in strong magnetic fields is central for a microscopic interpretation of the integer quantum Hall effect. Within the framework of the nonequilibrium Keldysh-Green's function formalism, we consider the general expressions of energy-resolved and space-resolved current distributions in Hall samples. Formal elaboration, corroborated also by numerical calculations, shows that chirality of current flow, thermodynamic equilibration of conductive channels, as well as conductance quantization, are all a straight consequence of the semilocal nature of retarded (or advanced) Green's functions in strong magnetic fields
Electronic conductance of one-dimensional chains with phonon dephasing disorder
No full textIn this paper we analyse how electron transport through a one-dimensional chain is modified by the presence of phonon dephasing mechanisms active in a limited strand of the chain. The treatment is based on the nonequilibrium Keldysh Green's function and the self-consistent first Born approximation, with a tight-binding description of the electronic states. A most remarkable feature of the calculated conductance curves is the occurrence of an exponential decrease for small lengths, followed by a slow asymptotic decrease inversely proportional to the strand length. The origin of such a different short-range and long-range behaviour of the conductance, and other observed scaling features, are interpreted with some intuitive understanding of the dephasing mechanisms
Electronic states and magnetotransport in unipolar and bipolar graphene ribbons
No full textThe electronic structure and the current profiles of n - and p -doped graphene ribbons are investigated within the Keldysh Green’s function method in the tight-binding framework. The low energy spectrum, at the heart of the relativisticlike quantum transport, is studied numerically and relevant features are understood analytically by means of the continued fraction tool. Simulations of charge transport and spatial distribution of spectral currents in field-effect controlled graphene ribbons are then carried out in the absence and in the presence of uniform magnetic fields. The role of gated regions and threading magnetic fields for manipulating the flow of Dirac particles is investigated
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