Institute of Molecular Physics, Polish Academy of Sciences, ulica Mariana Smoluchowskiego 17, 60-179 Poznań, Poland.
J Phys Condens Matter. 2011 May 4;23(17):175305. doi: 10.1088/0953-8984/23/17/175305. Epub 2011 Apr 15.
We study transport through a two-level quantum dot (QD) weakly coupled to ferromagnetic electrodes, the mutual magnetization orientation of which can be changed from a parallel to an antiparallel configuration. Calculations are performed in a sequential tunnelling regime taking into account an inter-level Coulomb and an exchange interaction on the QD with many-body electronic states. Our interests are mainly focused on the role of singlet and triplet states on the tunnel magnetoresistance (TMR). We have found that TMR characteristics strongly depend on different local spin configurations in the QD, which originate from an anti- or ferromagnetic exchange coupling J as well as its strength. A strong inter-channel Coulomb blockade (which influences the TMR) appears when the ground state is singly occupied. Activation of the singlet or the triplet states and competition between various tunnelling rates are responsible for the spin accumulation even in the parallel configuration. We have also found negative TMR and negative differential resistance (NDR) effects in the system with strong coupling asymmetry.
我们研究了通过弱耦合到铁磁电极的两层量子点（QD）的输运，其相互磁化方向可以从平行变为反平行配置。在考虑QD 上的能级间库仑和交换相互作用以及多体电子态的顺序隧道区域进行了计算。我们的兴趣主要集中在单态和三重态对隧道磁电阻（TMR）的作用上。我们发现，TMR 特性强烈依赖于QD 中不同的局部自旋配置，这些配置源于反铁或铁磁交换耦合 J 及其强度。当基态被单占据时，会出现强烈的跨通道库仑阻塞（影响 TMR）。单态或三重态的激活以及各种隧道速率之间的竞争是导致即使在平行配置中也存在自旋积累的原因。我们还在具有强耦合不对称性的系统中发现了负 TMR 和负微分电阻（NDR）效应。
