Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland.
J Phys Condens Matter. 2013 Feb 20;25(7):075301. doi: 10.1088/0953-8984/25/7/075301. Epub 2013 Jan 17.
We study the spin-resolved transport through single-level quantum dots strongly coupled to ferromagnetic leads in the Kondo regime, with a focus on contact and material asymmetry-related effects. By using the numerical renormalization group method, we analyze the dependence of relevant spectral functions, the linear conductance and the tunnel magnetoresistance on the system asymmetry parameters. In the parallel magnetic configuration of the device the Kondo effect is generally suppressed due to the presence of an exchange field, irrespective of the system's asymmetry. In the antiparallel configuration, on the other hand, the Kondo effect can develop if the system is symmetric. We show that even relatively weak asymmetry may lead to suppression of the Kondo resonance in the antiparallel configuration and thus give rise to nontrivial behavior of the tunnel magnetoresistance. In addition, by using the second-order perturbation theory we derive general formulas for the exchange field in both magnetic configurations of the system.
我们研究了在近藤 regime 下，强烈耦合到铁磁引线的单量子点的自旋分辨输运，重点关注接触和材料非对称相关的效应。通过使用数值重整化群方法，我们分析了相关谱函数、线性电导和隧道磁阻对系统非对称参数的依赖性。在器件的平行磁构型中，由于存在交换场，近藤效应通常会被抑制，而与系统的非对称性无关。另一方面，在反平行构型中，如果系统是对称的，近藤效应可以发展。我们表明，即使是较弱的非对称性也可能导致反平行构型中近藤共振的抑制，从而导致隧道磁阻的非平凡行为。此外，我们还通过二阶微扰理论推导出了系统在两种磁构型下的交换场的一般公式。
