Persistent spin current in nanodevices and definition of the spin current
Persistent spin current in nanodevices and definition of the spin current
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纳米器件中的持续自旋流及其定义
DOI：
10.1103/physrevb.77.035327
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发表时间：
2008-01-01
影响因子：
3.7
通讯作者：
Wang, Jian
中科院分区：
文献类型：
--
作者：
Sun, Qing-feng;Xie, X. C.;Wang, Jian
我们研究了两个密切相关的主题：（i）在具有自旋轨道相互作用（SOI）的半导体介观器件中存在纯持续自旋电流而不伴随电荷电流;（ii）在SOI存在下自旋电流的定义。通过四种不同物理图象的物理论证，有力地证明了在没有磁场和磁性材料的情况下，SOI器件中确实存在平衡的持续自旋电流。这种持续的自旋电流是一种模拟的持续电荷电流在介观环螺纹的磁通量，它描述了真实的自旋运动，可以通过实验测量。然后我们研究了自旋流的定义。我们指出：（i）在平衡SOI器件中的非零自旋电流是持续的自旋电流，（ii）自旋电流是，在一般情况下，不守恒，和（iii）违反Onsager关系的自旋输运无论使用什么定义的自旋电流。这些问题，非零自旋流在平衡的情况下，非保守的自旋流，违反昂萨格关系，是自旋输运的内在属性。我们注意到，自旋流的传统定义具有非常清晰的物理直观性，并且很好地描述了自旋运动。因此，我们认为自旋流的传统定义在物理上是有意义的，没有必要对其进行修改。（注意，这个结论与我们以前论文中的观点并不矛盾）。此外，还讨论了持续自旋电流与输运自旋电流的关系，混合环SOI区的持续线自旋电流和角自旋电流，以及持续自旋电流的测量。最后，我们表明，如果将自旋-自旋相互作用包含在汉密尔顿中，则使用传统定义，持续自旋流自动守恒。
We investigate two closely related subjects: (i) the existence of a pure persistent spin current without an accompanying charge current in a semiconducting mesoscopic device with a spin-orbit interaction (SOI) and (ii) the definition of the spin current in the presence of SOI. Through physical argument from four physical pictures in different aspects, we provide strong evidences that the equilibrium persistent spin current does exist in a device with SOI in the absence of any magnetic field or magnetic materials. This persistent spin current is an analog of the persistent charge current in a mesoscopic ring threaded by a magnetic flux, and it describes the real spin motion and can be measured experimentally. We then investigate the definition of the spin current. We point out that (i) the nonzero spin current in the equilibrium SOI device is the persistent spin current, (ii) the spin current is, in general, not conserved, and (iii) the Onsager relation is violated for the spin transport no matter what definition of the spin current is used. These issues, the nonzero spin current in the equilibrium case, the nonconserved spin current, and the violation of the Onsager relation, are intrinsic properties of spin transport. We note that the conventional definition of the spin current has very clear physical intuition and describes the spin motion very well. Therefore, we feel that the conventional definition of the spin current makes physical sense, and there is no need to modify it. (Note that this conclusion is not in contradiction with the opinions in our previous papers). In addition, the relationship between the persistent spin current and transport spin current, the persistent linear and angular spin currents in the SOI region of the hybrid ring, and the measurement of the persistent spin current are discussed. Finally, we show that if the spin-spin interaction is included into the Hamiltonian, the persistent spin current is automatically conserved using the conventional definition.