16,546 research outputs found
Relation between dispersion lines and conductance of telescoped armchair double-wall nanotubes analyzed using perturbation formulas and first-principles calculations
The Landauer's formula conductance of the telescoped armchair nanotubes is
calculated with the Hamiltonian defined by first-principles calculations
(SIESTA code). Herein, partially extracting the inner tube from the outer tube
is called 'telescoping'. It shows a rapid oscillation superposed on a slow
oscillation as a function of discrete overlap length with an integer
variable and the lattice constant . Considering the interlayer
Hamiltonian as a perturbation, we obtain the approximate formula of the
amplitude of the slow oscillation as where is
the effective interlayer interaction and is the band split
without interlayer interaction. The approximate formula is related to the
Thouless number of the dispersion lines.Comment: 9 figure
Scattering Theory for Quantum Hall Anyons in a Saddle Point Potential
We study the theory of scattering of two anyons in the presence of a
quadratic saddle-point potential and a perpendicular magnetic field. The
scattering problem decouples in the centre-of-mass and the relative
coordinates. The scattering theory for the relative coordinate encodes the
effects of anyon statistics in the two-particle scattering. This is fully
characterized by two energy-dependent scattering phase shifts. We develop a
method to solve this scattering problem numerically, using a generalized lowest
Landau level approximation.Comment: 5 pages. Published version, with clarified presentatio
Finite Conductivity in Mesoscopic Hall Bars of Inverted InAs/GaSb Quantum Wells
We have studied experimentally the low temperature conductivity of mesoscopic
size InAs/GaSb quantum well Hall bar devices in the inverted regime. Using a
pair of electrostatic gates we were able to move the Fermi level into the
electron-hole hybridization state, and observe a mini gap. Temperature
dependence of the conductivity in the gap shows residual conductivity, which
can be consistently explained by the contributions from the free as well as the
hybridized carriers in the presence of impurity scattering, as proposed by
Naveh and Laikhtman [Euro. Phys. Lett., 55, 545-551 (2001)]. Experimental
implications for the stability of proposed helical edge states will be
discussed.Comment: 5 pages, 4 figure
Efficient atomic self-interaction correction scheme for non-equilibrium quantum transport
Density functional theory calculations of electronic transport based on local
exchange and correlation functionals contain self-interaction errors. These
originate from the interaction of an electron with the potential generated by
itself and may be significant in metal-molecule-metal junctions due to the
localized nature of the molecular orbitals. As a consequence, insulating
molecules in weak contact with metallic electrodes erroneously form highly
conducting junctions, a failure similar to the inability of local functionals
of describing Mott-Hubbard insulators. Here we present a fully self-consistent
and still computationally undemanding self-interaction correction scheme that
overcomes these limitations. The method is implemented in the Green's function
non-equilibrium transport code Smeagol and applied to the prototypical cases of
benzene molecules sandwiched between gold electrodes. The self-interaction
corrected Kohn-Sham highest occupied molecular orbital now reproduces closely
the negative of the molecular ionization potential and is moved away from the
gold Fermi energy. This leads to a drastic reduction of the low bias current in
much better agreement with experiments.Comment: 4 pages, 5 figure
Conduction Mechanism in a Molecular Hydrogen Contact
We present first principles calculations for the conductance of a hydrogen
molecule bridging a pair of Pt electrodes. The transmission function has a wide
plateau with T~1 which extends across the Fermi level and indicates the
existence of a single, robust conductance channel with nearly perfect
transmission. Through a detailed Wannier function analysis we show that the H2
bonding state is not involved in the transport and that the plateau forms due
to strong hybridization between the H2 anti-bonding state and states on the
adjacent Pt atoms. The Wannier functions furthermore allow us to derive a
resonant-level model for the system with all parameters determined from the
fully self-consistent Kohn-Sham Hamiltonian.Comment: 5 pages, 4 figure
A theoretical model for single molecule incoherent scanning tunneling spectroscopy
Single molecule scanning tunneling spectroscopy (STS), with dephasing due to
elastic and inelastic scattering, is of some current interest. Motivated by
this, we report an extended Huckel theory (EHT) based mean-field
Non-equilibrium Green's function (NEGF) transport model with electron-phonon
scattering treated within the self-consistent Born approximation (SCBA).
Furthermore, a procedure based on EHT basis set modification is described. We
use this model to study the effect of the temperature dependent dephasing, due
to low lying modes in far-infrared range for which hw<<kT, on the resonant
conduction through highest occupied molecular orbital (HOMO) level of a phenyl
dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we
propose to include dephasing in room temperature molecular resonant conduction
calculations.Comment: 12 pages, 5 figure
The effect of vacancy-induced magnetism on electronic transport in armchair carbon nanotubes
The influence of local magnetic moment formation around three kinds of
vacancies on the electron conduction through metallic single-wall carbon
nanotubes is studied by use of the Landauer formalism within the coherent
regime. The method is based on the single-band tight-binding Hamiltonian, a
surface Green's function calculation, and the mean-field Hubbard model. The
numerical results show that the electronic transport is spin-polarized due to
the localized magnetic moments and it is strongly dependent on the geometry of
the vacancies. For all kinds of vacancies, by including the effects of local
magnetic moments, the electron scattering increases with respect to the
nonmagnetic vacancies case and hence, the current-voltage characteristic of the
system changes. In addition, a high value for the electron-spin polarization
can be obtained by applying a suitable gate voltage.Comment: 6 pages, 6 figure
Effect of dephasing on the current statistics of mesoscopic devices
We investigate the effects of dephasing on the current statistics of
mesoscopic conductors with a recently developed statistical model, focusing in
particular on mesoscopic cavities and Aharonov-Bohm rings. For such devices, we
analyze the influence of an arbitrary degree of decoherence on the cumulants of
the current. We recover known results for the limiting cases of fully coherent
and totally incoherent transport and are able to obtain detailed information on
the intermediate regime of partial coherence for a varying number of open
channels. We show that dephasing affects the average current, shot noise, and
higher order cumulants in a quantitatively and qualitatively similar way, and
that consequently shot noise or higher order cumulants of the current do not
provide information on decoherence additional or complementary to what can be
already obtained from the average current.Comment: 4 pages, 4 figure
Electrical Conductance of Molecular Wires
Molecular wires (MW) are the fundamental building blocks for molecular
electronic devices. They consist of a molecular unit connected to two continuum
reservoirs of electrons (usually metallic leads). We rely on Landauer theory as
the basis for studying the conductance properties of MW systems. This relates
the lead to lead current to the transmission probability for an electron to
scatter through the molecule. Two different methods have been developed for the
study of this scattering. One is based on a solution of the Lippmann-Schwinger
equation and the other solves for the {\bf t} matrix using Schroedinger's
equation. We use our methodology to study two problems of current interest. The
first MW system consists of 1,4 benzene-dithiolate (BDT) bonded to two gold
nanocontacts. Our calculations show that the conductance is sensitive to the
chemical bonding between the molecule and the leads. The second system we study
highlights the interesting phenomenon of antiresonances in MW. We derive an
analytic formula predicting at what energies antiresonances should occur in the
transmission spectra of MW. A numerical calculation for a MW consisting of
filter molecules attached to an active molecule shows the existence of an
antiresonance at the energy predicted by our formula.Comment: 14 pages, 5 figure
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