13 research outputs found
Chiral currents in gold nanotubes
Results are presented for the electron current in gold chiral nanotubes
(AuNTs). Starting from the band structure of (4,3) and (5,3) AuNTs, we find
that the magnitude of the chiral currents are greater than those found in
carbon nanotubes. We also calculate the associated magnetic flux inside the
tubes and find this to be higher than the case of carbon nanotubes. Although
(4,3) and (5,3) AuNTs carry transverse momenta of similar magnitudes, the
low-bias magnetic flux carried by the former is far greater than that carried
by the latter. This arises because the low-bias longitudinal current carried by
a (4,3) AuNT is significantly smaller than that of a (5,3) AuNT.Comment: 5 pages, 6 figure
Quantum Interference in Single Molecule Electronic Systems
We present a general analytical formula and an ab initio study of quantum
interference in multi-branch molecules. Ab initio calculations are used to
investigate quantum interference in a benzene-1,2-dithiolate (BDT) molecule
sandwiched between gold electrodes and through oligoynes of various lengths. We
show that when a point charge is located in the plane of a BDT molecule and its
position varied, the electrical conductance exhibits a clear interference
effect, whereas when the charge approaches a BDT molecule along a line normal
to the plane of the molecule and passing through the centre of the phenyl ring,
interference effects are negligible. In the case of olygoynes, quantum
interference leads to the appearance of a critical energy , at which the
electron transmission coefficient of chains with even or odd numbers of
atoms is independent of length. To illustrate the underlying physics, we derive
a general analytical formula for electron transport through multi-branch
structures and demonstrate the versatility of the formula by comparing it with
the above ab-initio simulations. We also employ the analytical formula to
investigate the current inside the molecule and demonstrate that large counter
currents can occur within a ring-like molecule such as BDT, when the point
charge is located in the plane of the molecule. The formula can be used to
describe quantum interference and Fano resonances in structures with branches
containing arbitrary elastic scattering regions connected to nodal sites.Comment: 12 pages, 11 figure
GOLLUM: a next-generation simulation tool for electron, thermal and spin transport
We have developed an efficient simulation tool 'GOLLUM' for the computation
of electrical, spin and thermal transport characteristics of complex
nanostructures. The new multi-scale, multi-terminal tool addresses a number of
new challenges and functionalities that have emerged in nanoscale-scale
transport over the past few years. To illustrate the flexibility and
functionality of GOLLUM, we present a range of demonstrator calculations
encompassing charge, spin and thermal transport, corrections to density
functional theory such as LDA+U and spectral adjustments, transport in the
presence of non-collinear magnetism, the quantum-Hall effect, Kondo and Coulomb
blockade effects, finite-voltage transport, multi-terminal transport, quantum
pumps, superconducting nanostructures, environmental effects and pulling curves
and conductance histograms for mechanically-controlled-break-junction
experiments.Comment: 66 journal pages, 57 figure
Symmetry-induced interference effects in metalloporphyrin wires
Organo-metallic molecular structures where a single metallic atom is embedded
in the organic backbone are ideal systems to study the effect of strong
correlations on their electronic structure. In this work we calculate the
electronic and transport properties of a series of metalloporphyrin molecules
sandwiched by gold electrodes using a combination of density functional theory
and scattering theory. The impact of strong correlations at the central
metallic atom is gauged by comparing our results obtained using conventional
DFT and DFT+U approaches. The zero bias transport properties may or may not
show spin-filtering behavior, depending on the nature of the d state closest to
the Fermi energy. The type of d state depends on the metallic atom and gives
rise to interference effects that produce different Fano features. The
inclusion of the U term opens a gap between the d states and changes
qualitatively the conductance and spin-filtering behavior in some of the
molecules. We explain the origin of the quantum interference effects found as
due to the symmetry-dependent coupling between the d states and other molecular
orbitals and propose the use of these systems as nanoscale chemical sensors. We
also demonstrate that an adequate treatment of strong correlations is really
necessary to correctly describe the transport properties of metalloporphyrins
and similar molecular magnets
GOLLUM: a next-generation simulation tool for electron, thermal and spin transport
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.-- et al.We have developed an efficient simulation tool 'GOLLUM' for the computation of electrical, spin and thermal transport characteristics of complex nanostructures. The new multi-scale, multi-terminal tool addresses a number of new challenges and functionalities that have emerged in nanoscale-scale transport over the past few years. To illustrate the flexibility and functionality of GOLLUM, we present a range of demonstrator calculations encompassing charge, spin and thermal transport, corrections to density functional theory such as local density approximation +U (LDA+U) and spectral adjustments, transport in the presence of non-collinear magnetism, the quantum Hall effect, Kondo and Coulomb blockade effects, finite-voltage transport, multi-terminal transport, quantum pumps, superconducting nanostructures, environmental effects, and pulling curves and conductance histograms for mechanically-controlled break-junction experiments.The research presented here was funded by the Spanish Ministerio de Economía y Competitividad through the grant FIS2012–34858, by UK EPSRC grants EP/K001507/1, EP/J014753/1, EP/H035818/1, and by the European Union Marie-Curie Network ‘MOLESCO’. VMGS thanks the Spanish Ministerio de Economía y Competitividad for a Ramón y Cajal fellowship (RYC-2010–06053). LO has been supported by the Hungarian Scientic Research Fund No. K108676.Peer Reviewe
Advanced Simulation of Conductance Histograms Validated through Channel-Sensitive Experiments on Indium Nanojunctions
We demonstrate a self-contained methodology for predicting conductance histograms of atomic and molecular junctions. Fast classical molecular-dynamics simulations are combined with accurate density functional theory calculations predicting both quantum transport properties and molecular-dynamics force field parameters. The methodology is confronted with experiments on atomic-sized indium nanojunctions. Beside conductance histograms the distribution of individual channel transmission eigenvalues is also determined by fitting the superconducting subgap features in the I-V curves. The remarkable agreement in the evolution of the channel transmissions demonstrates that the simulated ruptures are able to reproduce a realistic statistical ensemble of contact configurations, whereas simulations on selected ideal geometries show strong deviations from the experimental observations
Graphene sculpturene nanopores for DNA nucleobase sensing
et al.To demonstrate the potential of nanopores in bilayer graphene for DNA sequencing, we computed the current-voltage characteristics of a bilayer graphene junction containing a nanopore and found that they change significantly when nucleobases are transported through the pore. To demonstrate the sensitivity and selectivity of example devices, we computed the probability distribution PX(ß) of the quantity ß representing the change in the logarithmic current through the pore due to the presence of a nucleobase X (X = adenine, thymine, guanine, or cytosine). We quantified the selectivity of the bilayer-graphene nanopores by showing that P X(ß) exhibits distinct peaks for each base X. To demonstrate that such discriminating sensing is a general feature of bilayer nanopores, the well-separated positions of these peaks were shown to be present for different pores, with alternative examples of electrical contacts. © 2014 American Chemical Society.This work was supported by the European Union Marie-Curie Network MOLESCO. Funding was also provided by the UK EPSRC and the Spanish MINECO through Grant FIS2012-34858. V.G.-S. thanks the Spanish Ministerio de Economiá y Competitividad for a Ramón y Cajal fellowship (RYC-2010-06053).Peer Reviewe