二维IV族单硫族化合物MX（M：Sn，Ge; X：S，Se，Te）单分子膜中的本征持续自旋螺旋
Intrinsic persistent spin helix in two-dimensional group-IV monochalcogenide MX (M : Sn, Ge; X: S, Se, Te) monolayer
摘要：
节能自旋电子学被认为是可实现的系统托管持久自旋螺旋（PSH），因为它们支持一个非常长的自旋寿命的载流子。然而，实现PSH需要在动量空间中的单向自旋配置，由于微调Rashba和Dresselhaus自旋轨道耦合的严格条件，这实际上是不平凡的。在这里，我们预测PSH可以内在地实现在二维（2D）IV族单硫族化合物MX单层，一类新的非中心对称的2D材料具有面内铁电性。由于MX单层中的C2 v点群对称性，在面外方向上保持单向自旋配置，从而在[110]取向的量子阱中保持类似于[110] Dresselhaus模型的PSH。我们对不同MX（M：Sn，Ge; X：S，Se，Te）单分子膜的第一性原理计算证实，在价带最大值附近观察到了这种典型的自旋组态，在那里实现了相当大的自旋分裂和相当小的自旋极化波长。重要的是，我们观察到相反的面内铁电极化下的可逆的面外自旋取向，表明电可控PSH自旋电子应用是合理的。
英文摘要：
Energy-saving spintronics are believed to be implementable on the systems hosting persistent spin helix (PSH) since they support an extraordinarily long spin lifetime of carriers. However, achieving the PSH requires a unidirectional spin configuration in the momentum space, which is practically non-trivial due to the stringent conditions for fine-tuning the Rashba and Dresselhaus spin-orbit couplings. Here, we predict that the PSH can be intrinsically achieved on a two-dimensional (2D) group-IV monochalcogenide M X monolayer, a new class of the noncentrosymmetric 2D materials having in-plane ferroelctricity. Due to the C2v point group symmetry in the MX monolayer, a unidirectional spin configuration is preserved in the out-of-plane direction and thus maintains the PSH that is similar to the [110] Dresselhaus model in the [110]-oriented quantum well. Our first-principle calculations on various MX (M : Sn, Ge; X: S, Se, Te) monolayers confirmed that such typical spin configuration is observed, in particular, at near the valence band maximum where a sizable spin splitting and a substantially small wavelength of the spin polarization are achieved. Importantly, we observe reversible out-of-plane spin orientation under opposite in-plane ferroelectric polarization, indicating that an electrically controllable PSH for spintronic applications is plausible.
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