电子关联效应对平行双量子点系统磁输运性质的影响∗

摘要

从理论上研究了平行双量子点系统中的电子关联效应对该系统磁输运性质的影响。基于广义主方程方法，计算了通过此系统的电流、微分电导和隧穿磁阻。计算结果表明：电子自旋关联效应可以促发一个很大的隧穿磁阻，而电子库仑关联效应不仅可以压制电子自旋关联效应，还可以导致负隧穿磁阻和负微分电导的出现。对相关的基本物理问题进行了讨论。%We theoretically investigate the effects of electronic correlations (including spin and Coulomb correlations) on the magnetotransport through a parallel double quantum dot (DQD) coupled to ferromagnetic leads. Two dots couple coherently through electron correlations, rather than tunneling directly between two dots, and each dot is coupled to two semi-infinite ferromagnetic leads. We assume that the intradot Coulomb repulsion is much larger than the interdot Coulomb repulsion U . Thus, only the zero, one and two-particle DQD states are relevant to transport. Because of interdot electron correlation, the I-V characteristics of each dot is sensitive to the change in the state of the other dot. This work focuses on the effects of electron spin correlation and electron Coulomb correlation on magnetotransport through this system. In order to determine the transport properties of the system, we use the generalized master equation method. This method is based on the reduced density operator defined by averaging the statistical operator of the total system over the states of all leads. With the framework of the generalized master equation and the sequential tunneling approximation, we calculate the current, differential conductance and tunnel magnetoresistance (TMR) in the dot 1 as a function of bias for different spin correlations and Coulomb correlations. Our results reveal that the magnetotransport through this system is more sensitive to Coulomb correlation than to spin correlation;when Coulomb correlation equals zero, the spin correlation can induce a giant tunnel magnetoresistance, which is further larger than the Julliere’s value of TMR; when Coulomb correlation occurs, the giant tunnel magnetoresistance disappears; when Coulomb correlation is equal to or larger than spin correlation, Coulomb correlation can suppress spin correlation; while the coexistence of Coulomb correlation and asymmetry of the DQD system can result in dynamical channel blockade, which can lead to the occurrence of negative tunnel magetoresistance and negative differential conductance. These novel properties lead to the potential applications in nanoelectronics, and relevant underlying physics of this problem is discussed.