Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany.
J Phys Condens Matter. 2012 Jul 4;24(26):266003. doi: 10.1088/0953-8984/24/26/266003. Epub 2012 Jun 7.
The Keldysh nonequilibrium Green's function method is utilized to theoretically study spin-polarized transport through a graphene spin valve irradiated by a monochromatic laser field. It is found that the bias dependence of the differential conductance exhibits successive peaks corresponding to the resonant tunneling through the photon-assisted sidebands. The multi-photon processes originate from the combined effects of the radiation field and the graphene tunneling properties, and are shown to be substantially suppressed in a graphene spin valve which results in a decrease of the differential conductance for a high bias voltage. We also discuss the appearance of a dynamical gap around zero bias due to the radiation field. The gap width can be tuned by changing the radiation electric field strength and the frequency. This leads to a shift of the resonant peaks in the differential conductance. We also demonstrate numerically the dependences of the radiation and spin valve effects on the parameters of the external fields and those of the electrodes. We find that the combined effects of the radiation field, the graphene and the spin valve properties bring about an oscillatory behavior in the tunnel magnetoresistance, and this oscillatory amplitude can be changed by scanning the radiation field strength and/or the frequency.
利用克尔德什非平衡格林函数方法，从理论上研究了在单色激光场照射下通过石墨烯自旋阀的自旋极化输运。结果发现，微分电导的偏压依赖性表现出与光子辅助边带共振隧穿对应的连续峰值。多光子过程源于辐射场和石墨烯隧穿特性的综合效应，并且在导致高偏压下微分电导减小的石墨烯自旋阀中被显著抑制。我们还讨论了由于辐射场而在零偏压附近出现的动态间隙。通过改变辐射电场强度和频率，可以调节间隙宽度。这导致微分电导中的共振峰发生位移。我们还数值演示了辐射和自旋阀效应对外部场参数和电极参数的依赖性。我们发现，辐射场、石墨烯和自旋阀特性的综合效应导致隧穿磁电阻产生振荡行为，并且通过扫描辐射场强度和/或频率可以改变这种振荡幅度。
