Charging-induced asymmetry in molecular conductors
Charging-induced asymmetry in molecular conductors
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DOI：
10.1103/physrevb.70.245317
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发表时间：
2004-03
影响因子：
3.7
通讯作者：
F. Zahid;A. Ghosh;M. Paulsson;E. Polizzi;S. Datta
中科院分区：
文献类型：
--
作者：
F. Zahid;A. Ghosh;M. Paulsson;E. Polizzi;S. Datta
我们调查的起源不对称的各种测量的电流-电压$（I\text{\ensuremath{-}}V）$特性的分子没有固有的空间不对称性，特别是最近的重点突破结测量。我们认为，这种不对称性的出现是由于不平等的耦合与接触和随之而来的差异，在充电效果，这只能被捕获在一个自洽的模型分子传导。不对称的方向取决于分子中多数载流子的符号。对于通过最高占据分子轨道的传导（即，HOMO或$p$型传导），对于较强接触上的正电压，电流较小，而对于通过最低未占据分子轨道（即，LUMO或$n$型传导），则不对称的意义相反。在分子化学和接触微结构的扩展H“uckel描述中，（有两个可调参数，费米能的位置和硫-金键长），泊松方程的适当描述，和自洽耦合非平衡绿色函数描述的输运，我们实现了理论和实验$I\text{\ensuremath{-}}V$特性之间的良好协议，无论是在形状上还是在整体上。
We investigate the origin of asymmetry in various measured current-voltage $(I\text{\ensuremath{-}}V)$ characteristics of molecules with no inherent spatial asymmetry, with particular focus on a recent break junction measurement. We argue that such asymmetry arises due to unequal coupling with the contacts and a consequent difference in charging effects, which can only be captured in a self-consistent model for molecular conduction. The direction of the asymmetry depends on the sign of the majority carriers in the molecule. For conduction through highest occupied molecular orbitals (i.e., HOMO or $p$-type conduction), the current is smaller for positive voltage on the stronger contact, while for conduction through lowest unoccupied molecular orbitals (i.e., LUMO or $n$-type conduction), the sense of the asymmetry is reversed. Within an extended H\"uckel description of the molecular chemistry and the contact microstructure (with two adjustable parameters, the position of the Fermi energy and the sulphur-gold bond length), an appropriate description of Poisson's equation, and a self-consistently coupled nonequilibrium Green's function description of transport, we achieve good agreement between theoretical and experimental $I\text{\ensuremath{-}}V$ characteristics, both in shape as well as overall magnitude.