Transport through a mixed-valence molecular transistor in the sequential-tunneling regime: Theoretical insight from the two-site Peierls-Hubbard model (original) (raw)
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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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Proceedings of the National Academy of Sciences
Molecular junctions are essentially modified electrodes familiar to electrochemists where the electrolyte is replaced by a conducting "contact." It is generally hypothesized that changing molecular structure will alter system energy levels leading to a change in the transport barrier. Here, we show the conductance of seven different aromatic molecules covalently bonded to carbon implies a modest range (< 0.5 eV) in the observed transport barrier despite widely different free molecule HOMO energies (> 2 eV range). These results are explained by considering the effect of bonding the molecule to the substrate. Upon bonding, electronic inductive effects modulate the energy levels of the system resulting in compression of the tunneling barrier. Modification of the molecule with donating or withdrawing groups modulate the molecular orbital energies and the contact energy level resulting in a leveling effect that compresses the tunneling barrier into a range much smaller th...
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Physical Review B, 2005
We study electronic transport in diatomic molecules connected to metallic contacts in the regime where both electron-electron and electron-phonon interactions are important. We find that the competition between these interactions results in unique resonant conditions for interlevel transitions and polaron formation: the Coulomb repulsion requires additional energy when electrons attempt phonon-assisted interlevel jumps between fully or partially occupied levels. We apply the equations of motion approach to calculate the electronic Green's functions. The density of states and conductance through the system are shown to exhibit interesting Rabi-like splitting of Coulomb blockade peaks and strong temperature dependence under the interacting resonant conditions.
Theoretical Modeling of Tunneling Barriers in Carbon-Based Molecular Electronic Junctions
The Journal of Physical Chemistry C, 2015
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Coulomb interaction and transport in tunnel junctions and quantum dots
Physica B: Condensed Matter, 1993
In the first part of the paper the AC conductance of a quasi-one-dimensional tunnel junction involving a potential barrier is calculated in linear response. Its frequency dependence is used to define a dynamical capacitance. The influence of phase breaking electron-phonon interactions is investigated. It is argued that Coulomb interaction is of minor importance at higher frequencies and that dynamic and static capacitances are the same. The argument provides a high-frequency limit for turnstile operation. In the second part, the quantum mechanical properties of few interacting electrons in quantum dots are considered. Including the spin degree of freedom, the spectral properties of up to four interacting electrons confined within a quasi-one-dimensional system of finite length with Coulomb interactions are investigated by numerical diagonalization. The limitations of the description in terms of a capacitance are discussed. For sufficiently low density the electrons become localized, forming a Wigner molecule. The energetically lowest excitations are identified as vibrational and tunneling modes, both being collective modes involving all the electrons.
DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019
The quantum transport properties of a single molecular transistor are studied in the presence of an external magnetic field using the Keldysh Green function technique. The Anderson-Holstein-Caldeira-Leggett model is used to describe the single molecular transistor that consists of a molecular quantum dot (QD) coupled to two metallic leads and placed on a substrate that acts as a heat bath. The local electron-phonon (el-ph) interaction in the QD is decoupled by the Lang-Firsov (LF) transformation and the effective Hamiltonian is used to study the effects of an external magnetic field on the tunneling current and spin polarization of a SMT at zero temperature.
Molecular electronics: Some views on transport junctions and beyond
Proceedings of the National Academy of Sciences, 2005
The field of molecular electronics comprises a fundamental set of issues concerning the electronic response of molecules as parts of a mesoscopic structure and a technology-facing area of science. We will overview some important aspects of these subfields. The most advanced ideas in the field involve the use of molecules as individual logic or memory units and are broadly based on using the quantum state space of the molecule. Current work in molecular electronics usually addresses molecular junction transport, where the molecule acts as a barrier for incoming electrons: This is the fundamental Landauer idea of ''conduction as scattering'' generalized to molecular junction structures. Another point of view in terms of superexchange as a guiding mechanism for coherent electron transfer through the molecular bridge is discussed. Molecules generally exhibit relatively strong vibronic coupling. The last section of this overview focuses on vibronic effects, including inelastic electron tunneling spectroscopy, hysteresis in junction charge transport, and negative differential resistance in molecular transport junctions.