Coherent charge transport through molecular wires: Influence of strong Coulomb repulsion (original) (raw)
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2010
We consider exciton effects on current in molecular nanojunctions, using a model comprising a two two-level sites bridge connecting free electron reservoirs. Expanding the density operator in the many-electron eigenstates of the uncoupled sites, we obtain a 16X16 density matrix in the bridge subspace whose dynamics is governed by Liuoville equation that takes into account interactions on the bridge as well as electron injection and damping to and from the leads. Our consideration can be considerably simplified by using the pseudospin description based on the symmetry properties of Lie group SU(2). We study the influence of the bias voltage, the Coulomb repulsion and the energy-transfer interactions on the steady-state current and in particular focus on the effect of the excitonic interaction between bridge sites. Our calculations show that in case of non-interacting electrons this interaction leads to reduction in the current at high voltage for a homodimer bridge. In other words, w...
Theory of charge transport in molecular junctions: from Coulomb blockade to coherent tunneling
The Journal of chemical physics, 2014
We study charge transport through molecular junctions in the presence of electron-electron interaction using the nonequilibrium Green's function techniques and the renormalized perturbation theory. In the perturbation treatment, the zeroth-order Hamiltonian of the molecular junction is composed of independent single-impurity Anderson's models, which act as the channels where charges come through or occupy, and the interactions between different channels are treated as the perturbation. Using this scheme, the effects of molecule-lead, electron-electron, and hopping interactions are included nonperturbatively, and the charge transport processes can thus be studied in the intermediate parameter range from the Coulomb blockade to the coherent tunneling regimes. The concept of quasi-particles is introduced to describe the kinetic process of charge transport, and then the electric current can be studied and calculated. As a test study, the Hubbard model is used as the molecular Ha...
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2016
Nowadays, scientific issues have been focused on nanotechnology and properties of particular particle transport phenomena, and thus, atomistic-scale computations have been utilized in various research fields of physics, chemistry, biology, materials sciences, and engineering applications. In this thesis, we have developed a theoretical model to distinguish electrical conductance of molecular species in terms of current-voltage (I-V ) characteristics. A novel method to evaluate non-equilibrium electronic processes is proposed, which may overcome a computational barrier limited in ground states. Some numerical results from ab initio computations are also demonstrated, focusing on the orientation of molecules to the electrode surfaces in non-equilibrium transport processes, such as single-molecule junctions and oxygen reduction reactions (ORR). Our theoretical model is developed based on the Heisenberg uncertainty principle and numerical procedures in density functional theory. Further...
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Physical Review B, 2006
We identify experimental signatures in the current-voltage (I-V) characteristics of weakly contacted molecules directly arising from excitations in their many electron spectrum. The current is calculated using a multielectron master equation in the Fock space of an exact diagonalized model many-body Hamiltonian for a prototypical molecule. Using this approach, we explain several nontrivial features in frequently observed I-Vs in terms of a rich spectrum of excitations that may be hard to describe adequately with standard one-electron self-consistent field (SCF) theories.
Theory of quantum transport through molecular and atomic bridges
7th International Workshop on Computational Electronics. Book of Abstracts. IWCE (Cat. No.00EX427), 2000
Quantum electron transport through nano-structures such as metal atomic wires or molecular bridges is investigated with various theoretical approaches. The dierence of the quantization feature between Na and Al atom wires is explained based on the eigenchannel analyses combined with the recursion-transfer matrix calculation. The eigenchannels are calculated self-consistently for Au atom wires at ®nite bias voltage and the nonlinear conductance is explored in relation to the oset energies of d band channels. As for molecular bridges, we ®nd that a remarkable metalization is caused, if the coupling of the molecule with the metal electrode is enhanced. Internal current distribution within the molecular networks is discussed and exotic properties of the quantum transport is found. In particular, a strong induced loop current is revealed circulating the ring part of the molecule. The direction of the loop current is switched sharply when the electron incident energy sweeps a degenerate molecular level. 7
Physical Review B, 2010
We report a first-principles study of quantum transport in a prototype two-terminal device consisting of a molecular nanowire acting as an interconnect between two gold electrodes. The wire is composed of a series of bicyclo͓1.1.1͔pentane ͑BCP͒ cage-units. The length of the wire ͑L͒ is increased by sequentially increasing the number of BCP cage units in the wire from 1 to 3. A two terminal model device is made out of each of the three wires. A parameter free, nonequilibrium Green's function approach, in which the bias effect is explicitly included within a many body framework, is used to calculate the current-voltage characteristics of each of the devices. In the low bias regime that is considered in our study, the molecular devices are found to exhibit Ohmic behavior with resistances of 0.12, 1.4, and 6.5 ⍀ for the wires containing one, two, and three cages respectively. Thus the conductance value, G c , which is the reciprocal of resistance, decreases as e −L with a decay constant ͑͒ of 0.59 Å −1. This observed variation of conductance with the length of the wire is in excellent agreement with the earlier reported exponential decay feature of the electron transfer rate predicted from the electron transfer coupling matrix values obtained using the two-state Marcus-Hush model and the Koopman's theorem approximation. The downright suppression of the computed electrical current for a bias up to 0.4 V in the longest wire can be exploited in designing a three terminal molecular transistor; this molecular wire could potentially be used as a throttle to avoid leakage gate current.
Photoconductance from Exciton Binding in Molecular Junctions
Journal of the American Chemical Society, 2018
We report on a theoretical analysis and experimental verification of a mechanism for photoconductance, the change in conductance upon illumination, in symmetric single-molecule junctions. We demonstrate that photoconductance at resonant illumination arises due to the Coulomb interaction between the electrons and holes in the molecular bridge, so-called exciton-binding. Using a scanning tunneling microscopy break junction technique, we measure the conductance histograms of perylene tetracarboxylic diimide (PTCDI) molecules attached to Au-electrodes, in the dark and under illumination, and show a significant and reversible change in conductance, as expected from the theory. Finally, we show how our description of the photoconductance leads to a simple design principle for enhancing the performance of molecular switches.
Quantum Transport in Bridge Systems
Solid State Phenomena, 2009
We study electron transport properties of some molecular wires and a unconventional disordered thin film within the tight-binding framework using Green's function technique. We show that electron transport is significantly affected by quantum interference of electronic wave functions, molecule-to-electrode coupling strengths, length of the molecular wire and disorder strength. Our model calculations provide a physical insight to the behavior of electron conduction across a bridge system.
Optically induced current in molecular conduction nanojunctions with semiconductor contacts
Chemical Physics Letters, 2013
We propose a new approach to coherent control of transport via molecular junctions, which bypasses several of the hurdles to experimental realization of optically manipulated nanoelectronics noted in the previous literature. The method is based on the application of intrinsic semiconductor contacts and optical frequencies below the semiconductor bandgap. To explore the coherently controlled electronic dynamics, we introduce a density matrix formalism that accounts for both the discrete molecular state and the semiconductor quasicontinua within a single master equation and offers an analytically soluble limit. Our results illustrate the potential of semiconductor contacts in coherent control of photocurrent.