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纳米管量子点中偏转耦合引起的自旋弛豫

Spin relaxation due to deflection coupling in nanotube quantum dots

Mark S. Rudner, Emmanuel I. Rashba

备注：
Final version accepted for publication. References added.
发表信息：
Phys. Rev. B 81, 125426 (2010).
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摘要：

我们考虑了纳米管量子点中电子自旋的弛豫，由于它与弯曲声子模的耦合，并确定了一个新的自旋轨道介导的纳米管偏转和电子自旋之间的耦合。在小能量转移的极限下，这种机制优于其他自旋弛豫机制。由于长波长挠曲子的二次色散定律$ω\propto q^2$，态密度$dq/dω\propto ω^{-1/2}$发散为$ω\to 0$。此外，因为这里自旋直接耦合到纳米管偏转，所以与变形势耦合机制相比，存在$1/q$的因子的额外增强。我们发现，偏转耦合鲁棒地产生一个最小的自旋寿命$T_1$附近的避免交叉自旋轨道分裂水平在高温和低温限制的磁场依赖性。这提供了一种机制，该机制支持Churchill等人识别所观察到的$T_1$最小值，同时避免了单粒子谱中的交叉。[Phys. Rev. Lett. { \bf 102}，166802（2009）]。

英文摘要：

We consider relaxation of an electron spin in a nanotube quantum dot due to its coupling to flexural phonon modes, and identify a new spin-orbit mediated coupling between the nanotube deflection and the electron spin. This mechanism dominates other spin relaxation mechanisms in the limit of small energy transfers. Due to the quadratic dispersion law of long wavelength flexons, $ω\propto q^2$, the density of states $dq/dω\propto ω^{-1/2}$ diverges as $ω\to 0$. Furthermore, because here the spin couples directly to the nanotube deflection, there is an additional enhancement by a factor of $1/q$ compared to the deformation potential coupling mechanism. We show that the deflection coupling robustly gives rise to a minimum in the magnetic field dependence of the spin lifetime $T_1$ near an avoided crossing between spin-orbit split levels in both the high and low-temperature limits. This provides a mechanism that supports the identification of the observed $T_1$ minimum with an avoided crossing in the single particle spectrum by Churchill et al.[Phys. Rev. Lett. {\bf 102}, 166802 (2009)].

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