arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1909.08460cond-mat.mes-hallcond-mat.dis-nn
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量子自旋霍尔样品中边缘输运的保护:基于自旋对称性的一般方法和实例

Protection of Edge transport in Quantum Spin Hall samples: Spin-Symmetry Based General Approach and Examples

Oleg M. Yevtushenko, Vladimir I. Yudson

摘要:

理解可能的机制,这可能导致量子自旋霍尔(QSH)系统中螺旋边缘输运的抑制,在第一次实验揭示弹道电导的脆弱性之后引起了巨大的关注。尽管有非常深入的研究和丰富的理论模型,完全一致的解释实验结果仍然缺乏。我们系统化的螺旋运输的各种理论的帮助下,自旋守恒分析,它允许一个单独的设置与弹道电导被强大的保护,无论电子背散射。首先,我们简要地回顾了不同的理论在QSH样品的边缘输运的电子自旋轴对称性和不包括那些理论预测是不一致的自旋守恒分析,因此,需要更深入的研究。接下来,我们通过对代表性示例的详细研究来说明一般方法。其中一个地址的螺旋边缘耦合到一个阵列的海森堡相互作用的磁性杂质(MI),并表明,电导保持弹道,即使在边缘上的时间反演对称性(局部)打破,但总自旋是保守的。另一个例子着重于空间涨落自旋轨道相互作用对QSH边缘的影响。它揭示了在若干情况下保护的弱点,例如,U(1)对称的,但不是完全各向同性的,MI或一般的电子-电子相互作用的存在。

英文摘要:

Understanding possible mechanisms, which can lead to suppression of helical edge transport in Quantum Spin Hall (QSH) systems, attracted huge attention right after the first experiments revealing the fragility of the ballistic conductance. Despite the very intensive research and the abundance of theoretical models, the fully consistent explanation of the experimental results is still lacking. We systematize various theories of helical transport with the help of the spin conservation analysis which allows one to single out setups with the ballistic conductance being robustly protected regardless of the electron backscattering. First, we briefly review different theories of edge transport in the QSH samples with and without the spin axial symmetry of the electrons including those theoretical predictions which are not consistent with the spin conservation analysis and, thus, call for a deeper study. Next, we illustrate the general approach by a detailed study of representative examples. One of them addresses the helical edge coupled to an array of Heisenberg-interacting magnetic impurities (MIs) and demonstrates that the conductance remains ballistic even if the time-reversal symmetry on the edge is (locally) broken but the total spin is conserved. Another example focuses on the effects of the space-fluctuating spin-orbit interaction on the QSH edge. It reveals weakness of the protection in several cases, including, e.g., the presence of either the U(1)-symmetric, though not fully isotropic, MIs or generic electron-electron interactions.

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