自旋霍爾效應設置下在微結構附近產生的殘餘電阻偶極和電子自旋偶極的共振現象

Abstract

此論文的焦點放在一個有外加電場的微結構附近，自旋軌道交互作用對電荷和電子自旋的堆積的影響。透過一個環形的微結構所可能造成的量子共振效應，我們進一步探討放大自旋軌道交互作用的可能性。 最重要的發現是，以往一直被忽略的，由電位梯度產生的自旋軌道耦合可以使一個微結構附近造成可觀的電子自旋堆積。藉由把在一個外電場中非平衡電自分佈裡所有電子波的空間機率加總，我們可以在量子彈道範圍內的微結構附近得到一個狀似偶極的電子自旋分佈，也就是自旋偶極。伴隨著量子散射的共振，此交互作用可以提供我們一個調控自旋偶極的方法。特別的是，隨著系統費米能的改變，自旋偶極會表現出方向的反轉和強度的放大。 藉由引入一個與自旋相關的非平衡電子分佈，材料背景雜質所產生的外秉自旋軌道耦合效應已經包含在我們的考慮裡面。此效應在共振時對自旋偶極的修正並沒有值得注意的貢獻。

This thesis focuses on spin-orbit interaction effect on charge and spin accumulation around a microstructure in an external electric field. Furthermore, a ring type microstructure is introduced to explore possible amplification of the spin-orbit interaction effect from quantum resonances allowed by such microstructures.

A major finding in this thesis is that the mostly overlooked spin-orbit interaction arising from in-plane potential gradient can contribute to significant spin accumulation around a microstructure. By considering quantum-mechanical scattering of individual electrons in a nonequilibrium distribution acted upon by an external electric field, we obtain a spin dipole, or spin accumulation of a dipole-like spatial variation, around a microstructure within the ballistic range. The subsequent quantum scattering resonance provides and additional knob for the manipulation of spin dipole. Specifically, the spin dipole manifests both sign reversal and large amplification when the Fermi energy crosses a resonance.

We have included the extrinsic spin-orbit interaction effects from background spin-orbit scatterers by invoking a spin dependent nonequilibrium electron distribution. The correction of the spin dipole is found to be insignificant in the resonant region.