Floquet spin states in graphene under ac driven spin-orbit interaction
Floquet spin states in graphene under ac driven spin-orbit interaction
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DOI：
10.1103/physrevb.85.205428
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发表时间：
2012-04
影响因子：
3.7
通讯作者：
A. L'opez;Z. Sun;J. Schliemann
中科院分区：
文献类型：
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作者：
A. L'opez;Z. Sun;J. Schliemann
我们研究了单层石墨烯样品上周期性驱动的时间依赖的Rashba自旋轨道耦合（RSOC）的作用。在将原来的4 × 4动力学方程组转化为两个时间反演的两能级问题后，通过各种方法和近似方法研究了准能谱和相关动力学.在静态情况下，系统在狄拉克点处是带隙的。旋转波近似（RWA）适用于驱动系统非物理地保留了这一功能，而马格努斯-Floquet方法以及数值精确的评估Floquet方程表明，这个差距是动态关闭。另外，对于在静态极限下完全非极化的态，在驱动情况下发现了一个相当大的面外自旋极化的振荡模式。自相关函数的评估表明，原来的均匀干涉图案对应于时间无关的RSOC得到扭曲。由此产生的结构可以定性地解释为由交流驱动引起的静态本征态之间的跃迁的结果，即，这些跃迁调制相对相位，所述相对相位相加以给出自相关函数的量子恢复。与静态情况相反，在驱动场景中，量子复苏（抑制）与自旋上升（下降）阶段相关。
We study the role of periodically driven time-dependent Rashba spin-orbit coupling (RSOC) on a monolayer graphene sample. After recasting the originally $4\times 4$ system of dynamical equations as two time-reversal related two-level problems, the quasi-energy spectrum and the related dynamics are investigated via various techniques and approximations. In the static case the system is a gapped at the Dirac point. The rotating wave approximation (RWA) applied to the driven system unphysically preserves this feature, while the Magnus-Floquet approach as well as a numerically exact evaluation of the Floquet equation show that this gap is dynamically closed. In addition, a sizable oscillating pattern of the out-of-plane spin polarization is found in the driven case for states which completely unpolarized in the static limit. Evaluation of the autocorrelation function shows that the original uniform interference pattern corresponding to time-independent RSOC gets distorted. The resulting structure can be qualitatively explained as a consequence of the transitions induced by the ac driving among the static eigenstates, i.e., these transitions modulate the relative phases that add up to give the quantum revivals of the autocorrelation function. Contrary to the static case, in the driven scenario, quantum revivals (suppresions) are correlated to spin up (down) phases.