无序轴子绝缘体薄膜中的耗散边缘输运
Dissipative Edge Transport in Disordered Axion Insulator Films
AI总结：
本文结合第一性原理计算与 Landauer-Büttiker 输运分析，揭示无序使偶数层 MnBi$_2$Te$_4$ 的有能隙螺旋边缘态变为耗散无能隙态，并提出实验验证方案。
摘要：
我们研究了无序在轴子绝缘体薄膜边缘输运中的作用。通过第一性原理计算，我们预测偶数层 MnBi$_2$Te$_4$ 具有有能隙的螺旋边缘态。随机势将显著改变边缘谱函数，使其变为无能隙。然而，这里的这种无能隙螺旋态与量子自旋霍尔绝缘体或拓扑 Anderson 绝缘体中的无能隙螺旋态存在根本不同。我们进一步利用 Landauer-Büttiker 形式体系研究该系统中的边缘输运，发现这种无能隙边缘态是耗散性的，且不能免疫背散射，这可以解释实验中在六个七倍层 MnBi$_2$Te$_4$ 的轴子绝缘体态内观察到的耗散非局域输运。文中提出了若干输运实验，以验证我们关于耗散螺旋边缘通道的理论。特别是，即使增加一个额外的浮动探针且不使用它，纵向电阻也可大幅降低。这些结果将有助于在轴子绝缘体中观察人们长期寻求的拓扑磁电效应。
英文摘要：
We investigate the role of disorder in the edge transport of axion insulator films. We predict by first-principles calculations that even-number-layer MnBi$_2$Te$_4$ have gapped helical edge states. The random potential will dramatically modify the edge spectral function to become gapless. However, such gapless helical state here is fundamentally different from that in quantum spin Hall insulator or topological Anderson insulator. We further study the edge transport in this system by Landauer-Büttiker formalism, and find such gapless edge state is dissipative and not immune to backscattering, which would explain the dissipative nonlocal transport in the axion insulator state observed in six septuple layer MnBi$_2$Te$_4$ experimentally. Several transport experiments are proposed to verify our theory on the dissipative helical edge channels. In particular, the longitudinal resistance can be greatly reduced by adding an extra floating probe even if it is not used. These results will facilitate the observsation of long-sought topological magnetoelectric effect in axion insulators.
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