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Edge-state transport in Floquet topological insulators

机译：Floquet拓扑绝缘子的边缘态传输

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Floquet topological insulators are systems in which the topology emerges only when a time-periodic perturbation is applied. In these systems one can define quasienergy states which replace the equilibrium stationary states. The system exhibits its nontrivial topology by developing edge-localized quasienergy states which lie in a gap of the quasienergy spectrum. These states represent a nonequilibrium analog of the topologically protected edge states in equilibrium topological insulators which exhibit an edge conductance of 2e~2/h. Here we explore the transport properties of the edge states in a Floquet topological insulator. In stark contrast to the equilibrium result, we find that the two-terminal conductivity of these edge states is significantly different from 2e~2/h. This fact notwithstanding, we find that for certain external potential strengths the conductivity is smaller than 2e~2/h and robust to the effects of disorder and smooth changes to the Hamiltonian's parameters. This robustness is reminiscent of the robustness found in equilibrium topological insulators. We provide an intuitive understanding of the reduction of the conductivity in terms of a picture where electrons in edge states are scattered by photons. We also consider the Floquet sum rule [A. Kundu and B. Seradjeh, Phys. Rev. Lett. 111, 136402 (2013)], which was proposed in a different context. The summed conductivity recovers the equilibrium value of 2e~2/ h whenever edge states are present. We show that this sum rule holds in our system using both numerical and analytic techniques.
机译：浮球拓扑绝缘体是仅在应用时间周期扰动时才会出现拓扑的系统。在这些系统中，可以定义替代平衡稳态的准能态。该系统通过开发位于准能谱间隙中的边缘定位的准能态来展示其非平凡的拓扑。这些状态表示平衡拓扑绝缘子中受拓扑保护的边缘状态的非平衡类似物，其边缘电导为2e〜2 / h。在这里，我们探讨了Floquet拓扑绝缘体中边缘态的传输性质。与平衡结果形成鲜明对比的是，我们发现这些边缘态的两端电导率显着不同于2e〜2 / h。尽管如此，我们发现对于某些外部电势强度，电导率小于2e〜2 / h，并且对无序效应和哈密顿量参数的平稳变化具有鲁棒性。这种鲁棒性使人联想到平衡拓扑绝缘子中的鲁棒性。我们通过一张图片来直观地了解电导率的降低情况，其中处于边缘状态的电子被光子散射。我们还考虑了Floquet和规则[A. Kundu和B. Seradjeh，物理学。牧师111，136402（2013）]，这是在不同背景下提出的。每当存在边缘状态时，总的电导率恢复2e〜2 / h的平衡值。我们表明，使用数值和分析技术，该求和规则在我们的系统中均成立。

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  • 来源
    《Physical review》 |2016年第4期|045121.1-045121.11|共11页
  • 作者

    Aaron Farrell; T. Pereg-Barnea;

  • 作者单位

    Department of Physics and the Centre for Physics of Materials, McGill University, Montreal, Quebec, Canada H3A 2T8;

    Department of Physics and the Centre for Physics of Materials, McGill University, Montreal, Quebec, Canada H3A 2T8;

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