55 research outputs found
Many-body theory of electronic transport in single-molecule heterojunctions
A many-body theory of molecular junction transport based on nonequilibrium
Green's functions is developed, which treats coherent quantum effects and
Coulomb interactions on an equal footing. The central quantity of the many-body
theory is the Coulomb self-energy matrix of the junction.
is evaluated exactly in the sequential tunneling limit, and
the correction due to finite tunneling width is evaluated self-consistently
using a conserving approximation based on diagrammatic perturbation theory on
the Keldysh contour. Our approach reproduces the key features of both the
Coulomb blockade and coherent transport regimes simultaneously in a single
unified transport theory. As a first application of our theory, we have
calculated the thermoelectric power and differential conductance spectrum of a
benzenedithiol-gold junction using a semi-empirical -electron Hamiltonian
that accurately describes the full spectrum of electronic excitations of the
molecule up to 8--10eV.Comment: 13 pages, 7 figure
Coherent Destruction of Coulomb Blockade Peaks in Molecular Junctions
Coherent electronic transport in single-molecule junctions is investigated in
the Coulomb blockade regime. Both the transmission phase and probability are
calculated for junctions with various contact symmetries. A dramatic
suppression of the Coulomb blockade peaks is predicted for junctions where
multiple atomic orbitals of the molecule couple to a single electrode although
the charging steps are unaffected.Comment: 6 pages, 4 figure
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
Many-body theory of electronic transport in single-molecule heterojunctions
A many-body theory of molecular junction transport based on nonequilibrium
Green's functions is developed, which treats coherent quantum effects and
Coulomb interactions on an equal footing. The central quantity of the many-body
theory is the Coulomb self-energy matrix of the junction.
is evaluated exactly in the sequential tunneling limit, and
the correction due to finite tunneling width is evaluated self-consistently
using a conserving approximation based on diagrammatic perturbation theory on
the Keldysh contour. Our approach reproduces the key features of both the
Coulomb blockade and coherent transport regimes simultaneously in a single
unified transport theory. As a first application of our theory, we have
calculated the thermoelectric power and differential conductance spectrum of a
benzenedithiol-gold junction using a semi-empirical -electron Hamiltonian
that accurately describes the full spectrum of electronic excitations of the
molecule up to 8--10eV.Comment: 13 pages, 7 figure
Giant Thermoelectric Effect from Transmission Supernodes
We predict an enormous order-dependent quantum enhancement of thermoelectric
effects in the vicinity of a higher-order `supernode' in the transmission
spectrum of a nanoscale junction. Single-molecule junctions based on
3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The
nonequilibrium thermodynamic efficiency and power output of a thermoelectric
heat engine based on a 1,3-benzene junction are calculated using many-body
theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure
Effective Field Theory of Interacting \pi-Electrons
We develop a \pi-electron effective field theory (\pi-EFT) wherein the
two-body Hamiltonian for a \pi-electron system is expressed in terms of three
effective parameters: the \pi-orbital quadrupole moment, the on-site repulsion,
and a dielectric constant. As a first application of this \pi-EFT, we develop a
model of screening in molecular junctions based on image multipole moments, and
use this to investigate the reduction of the HOMO-LUMO gap of benzene. Beyond
this, we also use \pi-EFT to calculate the differential conductance spectrum of
the prototypical benzenedithiol-Au single-molecule junction and the
\pi-electron contribution to the van der Waals interaction between benzene and
a metallic electrode.Comment: 13 pages, 9 figure
A Molecular Platinum Cluster Junction: A Single-Molecule Switch
We present a theoretical study of the electronic transport through
single-molecule junctions incorporating a Pt6 metal cluster bound within an
organic framework. We show that the insertion of this molecule between a pair
of electrodes leads to a fully atomically engineered nano-metallic device with
high conductance at the Fermi level and two sequential high on/off switching
states. The origin of this property can be traced back to the existence of a
HOMO which consists of two degenerate and asymmetric orbitals, lying close in
energy to the Fermi level of the metallic leads. Their degeneracy is broken
when the molecule is contacted to the leads, giving rise to two resonances
which become pinned close to the Fermi level and display destructive
interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am.
Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ
Effect of Thermoelectric Cooling in Nanoscale Junctions
We propose a thermoelectric cooling device based on an atomic-sized junction.
Using first-principles approaches, we investigate the working conditions and
the coefficient of performance (COP) of an atomic-scale electronic refrigerator
where the effects of phonon's thermal current and local heating are included.
It is observed that the functioning of the thermoelectric nano-refrigerator is
restricted to a narrow range of driving voltages. Compared with the bulk
thermoelectric system with the overwhelmingly irreversible Joule heating, the
4-Al atomic refrigerator has a higher efficiency than a bulk thermoelectric
refrigerator with the same due to suppressed local heating via the
quasi-ballistic electron transport and small driving voltages. Quantum nature
due to the size minimization offered by atomic-level control of properties
facilitates electron cooling beyond the expectation of the conventional
thermoelectric device theory.Comment: 8 figure
Exact exchange-correlation potential of a ionic Hubbard model with a free surface
We use Lanczos exact diagonalization to compute the exact
exchange-correlation (xc) potential of a Hubbard chain with large binding
energy ("the bulk") followed by a chain with zero binding energy ("the
vacuum"). Several results of density functional theory in the continuum
(sometimes controversial) are verified in the lattice. In particular we show
explicitly that the fundamental gap is given by the gap in the Kohn-Sham
spectrum plus a contribution due to the jump of the xc-potential when a
particle is added. The presence of a staggered potential and a nearest-neighbor
interaction V allows to simulate a ionic solid. We show that in the ionic
regime in the small hopping amplitude limit the xc-contribution to the gap
equals V, while in the Mott regime it is determined by the Hubbard U
interaction. In addition we show that correlations generates a new potential
barrier at the surface
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