Bandwidth, intensity, and lineshape of the transmission spectrum in the single molecular junction (original) (raw)
Related papers
The Relation between Structure and Quantum Interference in Single Molecule Junctions
Nano Letters, 2010
Quantum interference (QI) of electron pathways has recently attracted increased interest as an enabling tool for singlemolecule electronic devices. Although various molecular systems have been shown to exhibit QI effects and a number of methods have been proposed for its analysis, simple guidelines linking the molecular structure to QI effects in the phase-coherent transport regime have until now been lacking. In the present work we demonstrate that QI in aromatic molecules is intimately related to the topology of the molecule's π system and establish a simple graphical scheme to predict the existence of QI-induced transmission antiresonances. The generality of the scheme, which is exact for a certain class of tight-binding models, is proved by a comparison to first-principles transport calculations for 10 different configurations of anthraquinone as well as a set of cross-conjugated molecular wires.
Quantum interference in off-resonant transport through single molecules
Physical Review B, 2014
We provide a simple set of rules for predicting interference effects in off-resonant transport through single-molecule junctions. These effects fall in two classes, showing respectively an odd or an even number of nodes in the linear conductance within a given molecular charge state, and we demonstrate how to decide the interference class directly from the contacting geometry. For neutral alternant hydrocarbons, we employ the Coulson-Rushbrooke-McLachlan pairing theorem to show that the interference class is decided simply by tunneling on and off the molecule from same, or different sublattices. More generally, we investigate a range of smaller molecules by means of exact diagonalization combined with a perturbative treatment of the molecule-lead tunnel coupling. While these results generally agree well with GW calculations, they are shown to be at odds with simpler mean-field treatments. For molecules with spin-degenerate ground states, we show that for most junctions, interference causes no transmission nodes, but argue that it may lead to a non-standard gate-dependence of the zero-bias Kondo resonance.
Transport properties of molecular junctions from many-body perturbation theory
Physical Review B, 2011
The conductance of single molecule junctions is calculated using a Landauer approach combined to many-body perturbation theory (MBPT) to account for electron correlation. The mere correction of the density-functional theory eigenvalues, which is the standard procedure for quasiparticle calculations within MBPT, is found not to affect noticeably the zero-bias conductance. To reduce it and so improve the agreement with the experiments, the wavefunctions also need to be updated by including the non-diagonal elements of the self-energy operator. PACS numbers: 85.65.+h, Most recent theoretical studies of coherent transport in nanojuctions are based on a Landauer approach [1], in which the electron interactions are treated at a simplified mean-field level using density-functional theory (DFT). While this approach has proven quite successful for systems having a strong coupling between the molecule and the metallic leads , it overestimates the zero-bias conductance of weakly coupled systems (by up to 3 orders of magnitude) compared to experimental measurements . Many explanations have been proposed for such a discrepancy. For example, arguing an uncertainty over the experimental junction structure, the sensitiveness to the contact geometry was investigated .
Many-body theory of electronic transport in single-molecule heterojunctions
Physical Review B Condensed Matter and Materials Physics, 2009
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 ΣC of the junction. ΣC 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 semiempirical π -electron Hamiltonian that accurately describes the full spectrum of electronic excitations of the molecule up to 8-10 eV.
An EHT based model for Single Molecule Incoherent Resonant Scanning Tunneling Spectroscopy
2007
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 Hückel 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 whichhω ≪ k B T , 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.
Connectivity dependence of Fano resonances in single molecules
Physical chemistry chemical physics : PCCP, 2017
Using a first principles approach combined with analysis of heuristic tight-binding models, we examine the connectivity dependence of two forms of quantum interference in single molecules. Based on general arguments, Fano resonances are shown to be insensitive to connectivity, while Mach-Zehnder-type interference features are shown to be connectivity dependent. This behaviour is found to occur in molecular wires containing anthraquinone units, in which the pendant carbonyl groups create Fano resonances, which coexist with multiple-path quantum interference features.
Physical Review B, 1987
A model is presented for the optical properties in the near to far infrared of a twofoldcommensurate one-dimensional system of noninteracting molecular-ion chains. Each chain may be subject to an arbitrary type of lattice distortion that doubles the periodicity of the regular chain and is composed of a lattice dimerization (LD) and/or an alternating molecular deformation (AMD). The effect of an external potential induced by the presence of nearby chains of closedshell counterions is also accounted for. The linear coupling of the electrons to an arbitrary number of intramolecular modes and to one longitudinal acoustic phonon branch is treated in the adiabatic linear-response approximation. No direct electron-electron interaction is explicitly included but the limit case of noninteracting spinless fermions in a large-U system can be dealt with in the present scheme. The results of the model can be directly applied to the analysis of the experimental infrared data of many conducting organic radical salts of 2:1 stoichiometry where LD and/or AMD of small amplitude occur and the on-site electron-electron correlation is thought to play a major role. The model fitting of the data can be used to obtain information on the one-electron bandwidth, the individual contributions to the total gap of charge density waves components centered on the bonds and on the sites, the relevance of the counterion potential, and the strength of the electron-phonon and electron-molecular vibration interactions. Some of these potentialities as well as the "selection rules" governing the infrared activity of the intramolecular and intermolecular modes as phase phonons are illustrated by numerical model calculations. Self-consistent relations and practical criteria that allow one to use the minimal number of adjustable parameters in the calculations are also presented.
Transmission eigenvalue distributions in highly conductive molecular junctions
Beilstein Journal of Nanotechnology, 2012
The transport through a quantum-scale device may be uniquely characterized by its transmission eigenvalues τ n . Recently, highly conductive single-molecule junctions (SMJ) with multiple transport channels (i.e., several τ n > 0) have been formed from benzene molecules between Pt electrodes. Transport through these multichannel SMJs is a probe of both the bonding properties at the lead-molecule interface and of the molecular symmetry.
Resonant transport and electrostatic effects in single-molecule electrical junctions
In this contribution we demonstrate structural control over a transport resonance in HS(CH 2) n [1,4 − C 6 H 4 ](CH 2) n SH (n = 1, 3, 4, 6) metal-molecule-metal junctions, fabricated and tested using the scanning tunneling microscopy-based I (z) method. The Breit-Wigner resonance originates from one of the arene π-bonding orbitals, which sharpens and moves closer to the contact Fermi energy as n increases. Varying the number of methylene groups thus leads to a very shallow decay of the conductance with the length of the molecule. We demonstrate that the electrical behavior observed here can be straightforwardly rationalized by analyzing the effects caused by the electrostatic balance created at the metal-molecule interface. Such resonances offer future prospects in molecular electronics in terms of controlling charge transport over longer distances, and also in single-molecule conductance switching if the resonances can be externally gated.
We develop a new general formulation to explore light-driven electron transport through a singlemolecule device with multiple pathways. Three individual systems are proposed including (i) a two-terminal molecular junction based on phenyl-acetylene macrocycle (PAM), (ii) PAM with three terminals, and (iii) a parallel molecular circuit. The computations show that PAM-based optoelectronic switches have robust large on-off ratios and weak-field operating conditions, which are not sensitive to asymmetric molecule-lead couplings. In addition, field-amplitude power laws for oneand two-photon assisted tunneling are evident in the computational results, and the laws can be proven by using perturbation analysis. For PAM-based optoelectronic routers, we show that it is possible to manipulate the direction of electric current through the PAM molecule by using a weak linearly polarized laser field. For parallel circuits made of molecular quantum dots, the condition of coherent destruction of tunneling is derived by using the rotating wave approximation and the high-frequency approximation.