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We highlight a new manifestation of quantum interference in transport through single-molecule junctions, owing to different charge transport pathways from the molecule through the contacts into the three-dimensional electrode. Such contact interference can be identified with characteristic features of the current–voltage curve, as dramatic as closing an otherwise open transport channel. Based on analysis of the necessary conditions for observation of this phenomenon, we conclude that this effect should be detectable in relatively small molecules, where a molecular site shares coupling to two electrodes, and an electrode surface site shares coupling to different molecular sites. The importance of the surface-molecule connectivity scheme implies that commonly used reduced models which couple different molecular sites to effectively independent electrodes, fail to account for this effect and must be corrected in order to properly capture contact interference. [ABSTRACT FROM AUTHOR]

Quantum transport in a fluctuating medium is often described using phenomenological time-dependent model Hamiltonians. Fitting the spectrum of the time-dependent forces onto a collection of oscillators, medium fluctuations can be mapped onto an interaction with a harmonic bath. In this framework, classical as well as quantum mechanical schemes can be applied to estimate averaged transport rates. Considering a generic two state model, a classical approach which relates a transfer rate to each fluctuation, and the total rate to an ensemble average, is shown to reproduce a standard rate expression. This expression turns out to be the high temperature limit of a quantum averaging scheme, which deviates from the classical result at finite temperature. The quantum averaging over fluctuating parameters is proposed here as an efficient and general approach to estimate the validity of quantum-classical simulations which treat quantum transport within an ensemble of molecular configurations generated by classical molecular dynamics. [ABSTRACT FROM AUTHOR]

The conductance through a branched conductor placed between two electrodes is analyzed using the Landauer transport formulation within the framework of the single electron, and the tight binding approximations. Terminal side chains are expressed as self energy terms which map the branched conductor onto an effective linear chain Hamiltonian. The effect of uniform side branches on resonant zero-bias conductance is shown to be analytically solvable and particularly simple, where subtraction or addition of a single terminal site can induce an effective discontinuity in the main linear chain or can effectively decouple the side branch from the conductor. Manipulating the "effective length" of a side branch by a local terminal gate potential, control of the small bias current through the branched conductor is demonstrated. [ABSTRACT FROM AUTHOR]