模拟有机分子线中的弹性和光辅助输运：长度依赖性和电流-电压特性
Modeling elastic and photoassisted transport in organic molecular wires: length dependence and current-voltage characteristics
摘要：
利用π轨道紧束缚模型，我们研究了基于不同长度的低聚亚苯基的金属-分子-金属结的弹性和光辅助输运性质。单色光的效果是用接触上的交流电压来模拟的。我们首先展示了如何低偏置的传输函数可以得到分析，使用以前采用的方法为简单的链模型。特别是，通过考虑有限长链和无限延伸的聚亚苯基来提取非谐振传输的衰减系数。基于这些分析结果，我们讨论了线性响应电导的长度依赖性，热电势，以及在弱强度和低频率的限制下的电导的光诱导增强。在一般情况下，电导增强数值计算作为光频率的函数。最后，我们计算在有限的直流电压的电流-电压特性，并表明，在低电压制度，低频光的效果是诱导电流阶跃的电压分离由两倍的频率。这些效应对于较长的分子更明显。我们研究了两种不同的配置文件的直流和交流电压，它被发现的结果是强大的，相对于这样的变化。虽然我们集中在这里的具体模型oligophenylenes，结果应该是定性类似的许多其他有机分子具有足够大的电子间隙。
英文摘要：
Using a pi-orbital tight-binding model, we study the elastic and photoassisted transport properties of metal-molecule-metal junctions based on oligophenylenes of varying lengths. The effect of monochromatic light is modeled with an ac voltage over the contact. We first show how the low-bias transmission function can be obtained analytically, using methods previously employed for simpler chain models. In particular, the decay coefficient of the off-resonant transmission is extracted by considering both a finite-length chain and infinitely extended polyphenylene. Based on these analytical results, we discuss the length-dependence of the linear-response conductance, the thermopower, and the light-induced enhancement of the conductance in the limit of weak intensity and low frequency. In general the conductance-enhancement is calculated numerically as a function of the light frequency. Finally, we compute the current-voltage characteristics at finite dc voltages, and show that in the low-voltage regime, the effect of low-frequency light is to induce current steps with a voltage separation determined by twice the frequency. These effects are more pronounced for longer molecules. We study two different profiles for the dc and ac voltages, and it is found that the results are robust with respect to such variations. Although we concentrate here on the specific model of oligophenylenes, the results should be qualitatively similar for many other organic molecules with a large enough electronic gap.
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