Spin Torque Effect in Mesoscopic Systems

自旋电子学是凝聚态物理学中的一个新兴领域，它的目标是在固体系统中利用电子自旋和电荷。到目前为止，已经提出了许多实现这一目标的想法。其中，对介观体系中的自旋力矩效应和自旋霍尔效应进行了深入的研究。我们得到了以下重要结果。Rashba自旋轨道(SO)耦合系统中的自旋力矩效应有效地产生了比普通自旋霍尔流大几个数量级的纯自旋流。在ESR驱动的量子点抽运的瞬时自旋电流中，表现出拉比振荡，反映了自旋态随时间的演化。由于横向限制引起的SO相互作用，在谐和量子线中形成螺旋边态，产生量子自旋霍尔(QSH)效应。QSH系统中的量子化电荷输运被任何弱磁无序破坏，而量子化和守恒的自旋输运在磁无序中幸存下来，只要体绝缘隙保持不变。

Spintronics is a burgeoning field in condensed matter physics which aims to harness electron spin in addition to charge in solid-sate systems. Many ideas for achieving this goal have been proposed to date. Among these, spin torque effect and spin Hall effect in mesoscopic systems are extensively investigated in this study. We obtain the following important results. The spin torque effect occurring in Rashba spin-orbit(SO) coupled systems efficiently produces a pure spin current which is orders of magnitude larger than ordinary spin Hall currents. Reflecting time evolution of spin state, a Rabi oscillation is exhibited in transient spin current pumped from a ESR-driven quantum dot. Helical edge states are formed in a harmonic quantum wire due to the SO interaction induced by lateral confinement, yielding the quantum spin Hall(QSH) effect. Quantized charge transport in the QSH system is destroyed by any weak magnetic disorder, whereas quantized and conserved spin transport survives magnetic disorder as long as bulk insulating gap remains intact.