Rudziński W
Department of Physics, Adam Mickiewicz University, ulica Umultowska 85, 61-614 Poznań, Poland.
J Phys Condens Matter. 2009 Jan 28;21(4):046005. doi: 10.1088/0953-8984/21/4/046005. Epub 2009 Jan 8.
Spin-polarized electronic tunneling through a quantum dot coupled to ferromagnetic electrodes is investigated within a nonequilibrium Green function approach. An interplay between coherent intradot spin-flip transitions, tunneling processes and Coulomb correlations on the dot is studied for current-voltage characteristics of the tunneling junction in parallel and antiparallel magnetic configurations of the leads. It is found that due to the spin-flip processes electric current in the antiparallel configuration tends to the current characteristics in the parallel configuration, thus giving rise to suppression of the tunnel magnetoresistance (TMR) between the threshold bias voltages at which the dot energy level becomes active in tunneling. Also, the effect of a negative differential conductance in symmetrical junctions, splitting of the conductance peaks, significant modulation of TMR peaks around the threshold bias voltages as well as suppression of the diode-like behavior in asymmetrical junctions is discussed in the context of coherent intradot spin-flip transitions. It is also shown that TMR may be inverted at selected gate voltages, which qualitatively reproduces the TMR behavior predicted recently for temperatures in the Kondo regime, and observed experimentally beyond the Kondo regime for a semiconductor InAs quantum dot coupled to nickel electrodes.
采用非平衡格林函数方法研究了通过与铁磁电极耦合的量子点的自旋极化电子隧穿。针对隧穿结在引线平行和反平行磁构型下的电流 - 电压特性，研究了量子点内相干自旋翻转跃迁、隧穿过程和库仑关联之间的相互作用。研究发现，由于自旋翻转过程，反平行构型中的电流趋于平行构型中的电流特性，从而导致在量子点能级在隧穿中变得活跃的阈值偏置电压之间，隧道磁电阻（TMR）受到抑制。此外，在相干量子点内自旋翻转跃迁的背景下，讨论了对称结中负微分电导的效应、电导峰的分裂、阈值偏置电压附近TMR峰的显著调制以及非对称结中类似二极管行为的抑制。研究还表明，在选定的栅极电压下TMR可能会反转，这定性地再现了最近针对近藤区温度预测的TMR行为，并且在实验中观察到，对于耦合到镍电极的半导体InAs量子点，在超越近藤区的情况下也存在这种行为。
