Rectification of laser-induced electronic transport through molecules

Lehmann, Jörg; Kohler, Sigmund; Hänggi, Peter; Nitzan, Abraham

doi:10.1063/1.1536639

Cited by 85 publications

(155 citation statements)

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“…The particular examples of systems displaying these phenomena are the ballistic regime in mesoscopic devices, various tunnel junctions, tunneling through quantum (molecular) wires, etc. Recently the directed current has been obtained for electrons that tunnel through the barrier containing the asymmetrically distributed energy levels in the presence of harmonic ac drive [16,17]. However, in this case the dissipation caused by the coupling to the leads is crucial in order to obtain a nonzero directed current.…”

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ac field-induced quantum rectification effect in tunnel junctions

2003

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We study the appearance of directed current in tunnel junctions (quantum ratchet effect), in the presence of an external ac field f (t). The current is established in a one-dimensional discrete inhomogeneous "tight-binding model". By making use of a symmetry analysis we predict the right choice of f (t) and obtain the directed current as a difference between electron transmission coefficients in opposite directions, ∆T = T LR − T RL . Numerical simulations confirm the predictions of the symmetry analysis and moreover, show that the directed current can be drastically increased by a proper choice of frequency and amplitudes of the ac field f (t).PACS numbers: 05.60. Gg, 73.23.Ad, 73.40.Gk A great attention has been devoted to theoretical and experimental studies of a transport rectification in various physical, chemical and biological systems [1,2]. In particular this peculiar effect appears in the form of a directed current as a system is exposed to a time-dependent ac force with zero mean. Such a directed motion (current) has been observed in molecular motors [1,3], in Josephson junction coupled systems [4,5], and in systems of cold Rb atoms in laser fields [6], just to name a few.In most studies the appearance of directed current has been analyzed by making use of the model of a particle moving in the presence of both space and time periodic potentials [2,7,8,9]. The effects of dissipation and interaction with a heat bath have been taken into account, and in many cases the decrease of dissipation as a system approaches the Hamiltonian limit, leads to a substantial increase of the directed current [9]. By making use of a symmetry analysis of the dynamic equations of motion it has been shown that the directed current occurs as a space-periodic potential is asymmetric (ratchet potential) and/or all important symmetries of an ac force, i.e. time-reversal and shift symmetry, are broken [2,9]. Notice here, that the latter case can be easier realized in experiments. It has been established that more complex systems described by generic Bolzman transport equation [10], Fokker-Planck equation [7,8,11], etc. also display a directed current. Moreover, the directed energy transport has been obtained in the case of interacting many particle systems described by nonlinear partial differential equations [12,13].Most previous studies analyzing both the dissipative and Hamiltonian limits, were heavily based on a classical nonlinear regime of particle motion. A next step is to obtain the directed transport in systems displaying quantum-mechanical behavior. The quantum regime of directed transport for a few particular systems has been studied in Refs. [5,14,15,16]. It was shown that a dissipationless quantum system in a single energy band tight-binding approximation does not support directed current [14], and although a quantum Brownian particle can display a directed motion and even numerous current reversal in the presence of an asymmetric ratchet potential, one still needs to take into account the dissipative effects [15]....

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ac field-induced quantum rectification effect in tunnel junctions

2003

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“…The laser irradiation induces a large current enhancement of several orders of magnitude and also can reduce the current noise level. The observation of these resonances could serve as an experimental starting point for the more challenging attempt of measuring quantum ratchet effects [7,8] or current switching by laser fields [9,10].…”

Section: Discussionmentioning

confidence: 99%

“…It is for example possible to induce by the laser field an oscillating current in the molecule which under certain asymmetry conditions is rectified by the molecule. This results in a directed electron transport even in the absence of any applied voltage [7,8]. Another theoretically predicted effect is the current suppression by the laser field [9,10] which offers the possibility to control both the average current and the current noise.…”

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Molecular Wires in Electromagnetic Fields

Kohler

Lehmann

Strass

et al. 2004

Advances in Solid State Physics 44

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Abstract. We investigate the role of external electromagnetic fields on the conduction properties of bridged molecular wires. In particular, it is analyzed quantitatively how resonant excitations of electrons enhance the dc current and, simultaneously, lower the noise level of the current. The results from an exact numerical treatment are in good agreement with those obtained within an approximation scheme applicable at resonances.Thirty years ago, Aviram and Ratner proposed in a seminal work [1] to build elements of electronic circuits-in their case a rectifier-with single molecules. In the present days their vision starts to become reality and the experimental and theoretical study of such systems enjoys a vivid activity [2][3][4]. Recent experimental progress has enabled reproducible measurements [5,6] of weak tunneling currents through molecules which are coupled by chemisorbed thiol groups to the gold surface of external leads.Typical energy scales in molecules are in the optical and the infrared regime, where basically all of the today's lasers operate. Hence, lasers represent a natural possibility to control atoms or molecules and also currents through them. It is for example possible to induce by the laser field an oscillating current in the molecule which under certain asymmetry conditions is rectified by the molecule. This results in a directed electron transport even in the absence of any applied voltage [7,8]. Another theoretically predicted effect is the current suppression by the laser field [9,10] which offers the possibility to control both the average current and the current noise.Since the considered frequencies lie below typical plasma frequencies of metals, the laser light will be reflected at the metal surface, i.e., it does not penetrate the leads. Consequently, we assume that the leads' bulk properties are essentially unaffected by the laser field-in particular each lead remains close to equilibrium. Thus, it is sufficient to consider the influence of the driving solely in the molecule Hamiltonian. In addition, the energy of infrared light quanta is by far smaller than the work function of a common metal, which is of the order of 5 eV. This prevents the generation of a photo current, which otherwise would dominate the effects discussed below. For a quantitative description of an experiment, it might be necessary to take into account also the influence of the laser on the leads.Most theoretical descriptions of the molecular conductivity in static situations are based on a scattering approach [11][12][13], or assume that the un-

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“…For a system for which the ac potential is spatially uniform in the driven region, the average current and the noise strength follow in the weak tunnelling limit already from the static conduction properties [21]. Especially for long wires, the master equation approach presented in [22,23] allows a more efficient numerical computation. The central idea behind this approach is to solve the coherent dynamics by means of a transformation into the basis given by the coherent Floquet states, i.e.…”

Section: Floquet Transport Theorymentioning

confidence: 99%

Controlling currents through molecular wires

Kohler

Lehmann

Hänggi

2003

Superlattices and Microstructures

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We investigate the possibility of controlling by means of external laser fields both the current through molecular wires and the corresponding noise properties. It is found that an appropriate off-resonant driving field reduces the coherent transport across the molecule resulting in a strong current suppression. The relative level of transport noise, characterized by a Fano factor, exhibits characteristic maxima and minima near regimes of current suppression. In a three-terminal configuration, the field allows one to steer the current selectively towards one terminal.

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Rectification of laser-induced electronic transport through molecules

Cited by 85 publications

References 56 publications

ac field-induced quantum rectification effect in tunnel junctions

ac field-induced quantum rectification effect in tunnel junctions

Molecular Wires in Electromagnetic Fields

Controlling currents through molecular wires

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