Interfacial charge and spin transport in Z2 topological insulators
Interfacial charge and spin transport in Z2 topological insulators
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DOI：
10.1103/physrevb.83.125401
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发表时间：
2010-09
影响因子：
3.7
通讯作者：
A. Yamakage;K. Imura;J. Cayssol;Y. Kuramoto
中科院分区：
文献类型：
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作者：
A. Yamakage;K. Imura;J. Cayssol;Y. Kuramoto
Kane-Mele模型实现了二维版本的Z2拓扑绝缘体作为石墨烯的理想化模型，具有内在和外在（Rashba）自旋轨道耦合。我们研究了这样一个狄拉克电子系统中存在一个锐电位阶跃即pn结时的电荷输运和自旋输运。当Rashba耦合占主导地位时，垂直于结入射的电子被完全反射，而当两种类型的耦合平衡时，它被完美地传输。后者在电荷输运中表现为电导的峰值和范诺因子的下降。电荷输运发生在与势垒垂直的方向上，而自旋电流是沿着势垒产生的，它也在势垒附近。结果表明，这种界面自旋霍尔电流是由带间矩阵元素和倏逝模式产生的。我们对自旋输运的分析是基于这样的观察，即在Rashba耦合消失的情况下，每个通道携带一个保守的自旋电流，而在一般情况下，只有集成的自旋电流是一个守恒量。电荷的完美透射/反射和自旋电流的守恒是反射对称的结果。最后，我们通过成像整个样品的流线和Veselago透镜（负折射）提供了电荷和自旋输运的准经典图像。
The Kane-Mele model realizes a two-dimensional version of a Z2 topological insulator as an idealized model of graphene with intrinsic and extrinsic (Rashba) spin-orbit couplings.We study the transport of charge and spin in such a Dirac electron system in the presence of a sharp potential step, that is, a pn junction. An electron incident normal to the junction is completely reflected when Rashba coupling is dominant, whereas it is perfectly transmitted when the two types of couplings are balanced. The latter manifests in charge transport as a peak of conductance and a dip in Fano factor. Charge transport occurs in the direction normal to the barrier, whereas a spin current is induced along the barrier that is also localized in its vicinity. It is demonstrated that contributions from interband matrix elements and evanescent modes are responsible for such an interfacial spin Hall current. Our analysis of spin transport is based on the observation that in the case of vanishing Rashba coupling, each channel carries a conserved spin current, whereas only the integrated spin current is a conserved quantity in the general case. The perfect transmission/reflection of charge and conserved spin current is a consequence of reflection symmetry. Finally, we provide a quasiclassical picture of charge and spin transport by imaging flow lines over the entire sample and Veselago lensing (negative refraction).