Electrical transport through a mechanically gated molecular wire
Electrical transport through a mechanically gated molecular wire
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DOI：
10.1103/physrevb.83.155402
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发表时间：
2011-04-01
影响因子：
3.7
通讯作者：
Tautz, F. S.
中科院分区：
文献类型：
--
作者：
Toher, C.;Temirov, R.;Tautz, F. S.
表面吸附的分子与扫描隧道显微镜（STM）的尖端在预定义的原子处接触。在尖端缩回时，分子从表面剥离。在这个实验中，一个二维微分电导图上测量的平面上跨越的偏置电压和尖端表面的距离。电导图表明，尖端缩回导致STM结中分子线的机械门控。实验进行了比较，一个详细的从头算模拟。我们发现，密度泛函理论（DFT）在局域密度近似（LDA）描述的尖端分子接触的形成和整个剥离过程中的分子结的几何形状的预测能力。然而，基于DFT-LDA的非平衡绿色函数（NEGF）形式主义的输运模拟未能描述的微分电导的行为，在实验中发现。进一步的分析表明，这种失败是由于平均场描述的电子关联的局域密度近似。这里提出的结果预计是普遍的有效性，并表明，对于广泛的常见的导线配置，模拟超出平均场水平，需要准确地描述通过分子的电流传导。最后，本研究的结果表明，良好的控制实验和并行从头计算输运模拟，系统地采样一个大的配置空间的分子-电极耦合允许在实验中的相关签名的明确识别。
A surface-adsorbed molecule is contacted with the tip of a scanning tunneling microscope (STM) at a predefined atom. On tip retraction, the molecule is peeled off the surface. During this experiment, a two-dimensional differential conductance map is measured on the plane spanned by the bias voltage and the tip-surface distance. The conductance map demonstrates that tip retraction leads to mechanical gating of the molecular wire in the STM junction. The experiments are compared with a detailed ab initio simulation. We find that density functional theory (DFT) in the local density approximation (LDA) describes the tip-molecule contact formation and the geometry of the molecular junction throughout the peeling process with predictive power. However, a DFT-LDA-based transport simulation following the nonequilibrium Green's function (NEGF) formalism fails to describe the behavior of the differential conductance as found in experiment. Further analysis reveals that this failure is due to the mean-field description of electron correlation in the local density approximation. The results presented here are expected to be of general validity and show that, for a wide range of common wire configurations, simulations which go beyond the mean-field level are required to accurately describe current conduction through molecules. Finally, the results of the present study illustrate that well-controlled experiments and concurrent ab initio transport simulations that systematically sample a large configuration space of molecule-electrode couplings allow the unambiguous identification of correlation signatures in experiment.