Simine Lena, Segal Dvira
Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 Saint George St. Toronto, Ontario M5S 3H6, Canada.
J Chem Phys. 2014 Jul 7;141(1):014704. doi: 10.1063/1.4885051.
We study electron transport in nanojunctions in which an electron on a quantum dot or a molecule is interacting with an N-state local impurity, a harmonic ("Holstein") mode, or a two-state system ("spin"). These two models, the Anderson-Holstein model and the spin-fermion model, can be conveniently transformed by a shift transformation into a form suitable for a perturbative expansion in the tunneling matrix element. We explore the current-voltage characteristics of the two models in the limit of high temperature and weak electron-metal coupling using a kinetic rate equation formalism, considering both the case of an equilibrated impurity, and the unequilibrated case. Specifically, we show that the analog of the Franck-Condon blockade physics is missing in the spin-fermion model. We complement this study by considering the low-temperature quantum adiabatic limit of the dissipative spin-fermion model, with fast tunneling electrons and a slow impurity. While a mean-field analysis of the Anderson-Holstein model suggests that nonlinear functionalities, bistability and hysteresis may develop, such effects are missing in the spin-fermion model at the mean-field level.
我们研究纳米结中的电子输运，其中量子点或分子上的电子与N态局域杂质、简谐（“霍尔斯坦”）模式或两态系统（“自旋”）相互作用。这两个模型，即安德森 - 霍尔斯坦模型和自旋 - 费米子模型，可以通过位移变换方便地转换为适合在隧穿矩阵元中进行微扰展开的形式。我们使用动力学速率方程形式，在高温和弱电子 - 金属耦合的极限下，研究这两个模型的电流 - 电压特性，同时考虑杂质平衡和非平衡的情况。具体而言，我们表明自旋 - 费米子模型中不存在类似于弗兰克 - 康登阻塞物理的现象。我们通过考虑具有快速隧穿电子和缓慢杂质的耗散自旋 - 费米子模型的低温量子绝热极限来补充这项研究。虽然安德森 - 霍尔斯坦模型的平均场分析表明可能会出现非线性功能、双稳性和滞后现象，但在平均场水平上，自旋 - 费米子模型中不存在这些效应。
