Spin Torque Effect in Mesoscopic Systems

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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.