Charge-memory polaron effect in molecular junctions

Physical review. B, Condensed matter (Impact Factor: 3.66). 02/2008; 78(8). DOI: 10.1103/PhysRevB.78.085409
Source: arXiv


The charge-memory effect, bistability and switching between charged and neutral states of a molecular junction, as observed in recent STM experiments, is considered within a minimal polaron model. We show that in the case of strong electron-vibron interaction the rate of spontaneous quantum switching between charged and neutral states is exponentially suppressed at zero bias voltage but can be tuned through a wide range of finite switching timescales upon changing the bias. We further find that, while junctions with symmetric voltage drop give rise to random switching at finite bias, asymmetric junctions exhibit hysteretic behavior enabling controlled switching. Lifetimes and charge-voltage curves are calculated by the master equation method for weak coupling to the leads and at stronger coupling by the equation-of-motion method for nonequilibrium Green functions. Comment: 4 pages, 5 figures, submitted

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Available from: Dmitry Ryndyk, Nov 12, 2012
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    • "Nuclear motions underlie the interplay between the coherent electron tunneling through the junction and inelastic thermally assisted hopping transport (Nitzan 2001). Also, electron-phonon interactions may result in polaronic conduction (Galperin 2005, Gutierrez 2005, Kubatkin 2003, Ryndyk 2008), and they are directly related to the junction heating (Segal 2003) and to some specific effects such as alterations in both shape of the molecule and its position with respect to the leads (Komeda 2002, Mitra 2004, Stipe 1999). The effects of electron-phonon interactions may be manifested in the inelastic tunneling spectrum which presents the second derivative of the current in the junction d 2 I/dV versus the applied voltage V. "
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    • "This method is an alternative to the Green function techniques earlier applied to the considered problem in Refs. [20] [23] [24] [25]. We start with the retarded Green function for two generic operators a and b which is defined as "
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    ABSTRACT: We analyze a single-level quantum system placed between metallic leads and strongly coupled to a localized vibrational mode, which models a singlemolecule junction or an STM setup. We consider a polaron model describing the interaction between electronic and vibronic degrees of freedom and develop and examine different truncation schemes in the equation-of-motion method within the framework of non-equilibrium Green functions. We show that upon applying gate or bias voltage, it is possible to observe charge-bistability and hysteretic behavior which can be the basis of a charge-memory element. We further perform a systematic analysis of the bistability behaviour of the system for different internal parameters such as the electron-vibron and the lead-molecule coupling strength. Comment: 12 pages, 5 figures
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