Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica, 8400 Bariloche, Argentina.
J Phys Condens Matter. 2012 Sep 12;24(36):365301. doi: 10.1088/0953-8984/24/36/365301. Epub 2012 Aug 15.
Starting from exact eigenstates for a symmetric ring, we derive a low-energy effective generalized Anderson Hamiltonian which contains two spin doublets with opposite momenta and a singlet for the neutral molecule. For benzene, the singlet (doublets) represent the ground state of the neutral (singly charged) molecule. We calculate the non-equilibrium conductance through a benzene molecule, doped with one electron or a hole (i.e. in the Kondo regime), and connected to two conducting leads at different positions. We solve the problem using the Keldysh formalism and the non-crossing approximation. When the leads are connected in the para position (at 180°), the model is equivalent to the ordinary impurity Anderson model and its known properties are recovered. For other positions, there is a partial destructive interference in the co-tunneling processes involving the two doublets and, as a consequence, the Kondo temperature and the height and width of the central peak (for bias voltage V(b) near zero) of the differential conductance G = dI/dV(b) (where I is the current) are reduced. In addition, two peaks at finite V(b) appear. We study the position of these peaks, the temperature dependence of G and the spectral densities. Our formalism can also be applied to carbon nanotube quantum dots with intervalley mixing.
从对称环的精确本征态出发，我们推导出一个低能有效广义安德森哈密顿量，它包含两个动量相反的自旋双重态和一个中性分子的单重态。对于苯，单重态（双重态）表示中性（单电荷）分子的基态。我们计算了通过掺杂一个电子或一个空穴（即在近藤区）的苯分子的非平衡电导，该分子连接到两个不同位置的导电引线。我们使用凯尔德什形式主义和非交叉近似来解决这个问题。当引线在para 位置（180°）连接时，该模型等效于普通的杂质安德森模型，并恢复其已知的性质。对于其他位置，涉及两个双重态的共隧道过程存在部分破坏性干涉，因此，近藤温度以及微分电导 G = dI/dV(b)（其中 I 是电流）的中央峰（对于偏置电压 V(b)接近零）的高度和宽度减小。此外，在有限 V(b)处出现两个峰。我们研究了这些峰的位置、G 的温度依赖性和谱密度。我们的形式主义也可以应用于具有区间混合的碳纳米管量子点。
