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arXiv 1104.4903cond-mat.mes-hall
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通过单分子接触的电荷转移:速率描述的可靠性如何?

Charge transfer through single molecule contacts: How reliable are rate descriptions?

Denis Kast, Lars Kecke, Joachim Ankerhold

摘要:

在过去的十年中,在纳米尺度上制造电路的趋势导致了分子电子学领域令人印象深刻的进展。然而,将分子接触作为未来器件的构建模块的理论描述是具有挑战性的,因为它必须将引线中费米液体的性质与分子上的电荷和声子自由度相结合。除了具体设置的从头算方案,通用模型揭示了运输过程的特点。特别吸引人的是成功地用于其他方面,如介观物理和分子内电子转移的转移速率的基础上的描述。然而,这个计划的详细分析与数值精确的数据相比是难以捉摸的。事实证明,一个公式在传输速率方面提供了一个定量准确的描述,即使在参数空间的域中,在严格意义上,它预计会失败,例如,较低的温度。通常,分子内声子根据电压驱动的稳态分布,其只能通过具有有效升高的温度(加热)的热分布粗略地捕获。扩展的主方程的电荷-声子复合物,有效地包括非对角元素的约化密度矩阵的影响,提供了非常准确的数据,甚至更强的电子-声子耦合。

英文摘要:

The trend to fabricate electrical circuits on nanoscale dimensions has led to impressive progress in the field of molecular electronics in the last decade. A theoretical description of molecular contacts as the building blocks of future devices is challenging though as it has to combine properties of Fermi liquids in the leads with charge and phonon degrees of freedom on the molecule. Apart from ab initio schemes for specific set-ups, generic models reveal characteristics of transport processes. Particularly appealing are descriptions based on transfer rates successfully used in other contexts such as mesoscopic physics and intramolecular electron transfer. However, a detailed analysis of this scheme in comparison with numerically exact data is elusive yet. It turns out that a formulation in terms of transfer rates provides a quantitatively accurate description even in domains of parameter space where in a strict sense it is expected to fail, e.g. for lower temperatures. Typically, intramolecular phonons are distributed according to a voltage driven steady state that can only roughly be captured by a thermal distribution with an effective elevated temperature (heating). An extension of a master equation for the charge-phonon complex to include effectively the impact of off-diagonal elements of the reduced density matrix provides very accurate data even for stronger electron-phonon coupling.

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