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arXiv 2407.02560cond-mat.str-elcond-mat.mes-hall
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Abelian 分数拓扑绝缘体何时可能存在于扭转 MoTe$_2$(及其他系统)中

When Could Abelian Fractional Topological Insulators Exist in Twisted MoTe$_2$ (and Other Systems)

Yves H. Kwan, Glenn Wagner, Jiabin Yu, Andrea Kouta Dagnino, Yi Jiang, Xiaodong Xu, B. Andrei Bernevig, Titus Neupert, Nicolas Regnault

AI总结:

本文利用精确对角化与 Landau 能级模型分析扭转 MoTe$_2$ 中 Abelian FTI 的稳定条件,指出短程排斥抑制和额外短程吸引的关键作用,并评估不同填充率与角度下的可行性。

摘要:

通过对 θ≈3.7° 扭转双层 MoTe$_2$(tMoTe$_2$)进行全面的精确对角化计算,并结合同样适用于更低 θ 的理想化 Landau 能级模型,我们提炼了在现实情形中设计分数拓扑绝缘体(FTI)的一般原则。首先,在 ν=1/3+1/3 的 Landau 能级设置中,我们研究相互作用的哪些特征会破坏 FTI。对于赝势相互作用和现实的屏蔽 Coulomb 相互作用,我们均发现,需要充分抑制短程排斥才能稳定 FTI。随后,我们研究具有现实能带混合和各向异性非局域介电屏蔽的 θ≈3.7° tMoTe$_2$。我们的有限尺寸计算仅在 ν=-4/3、且存在显著额外短程吸引 g(用于抵消短距离处的 Coulomb 排斥)时发现 FTI 相。我们讨论了进一步的有限尺寸漂移、介电工程、Landau 能级特征以及能带混合效应如何可能降低所需的 g 值,使其更接近 tMoTe$_2$ 的实验相关条件。向 n=1 Landau 能级的投影计算(该能级类似于 θ≃2.1° tMoTe$_2$ 的第二价带)对任何 g 都未产生 FTI,这表明低角度 tMoTe$_2$ 在 ν=-8/3 和 -10/3 处存在 FTI 的可能性或许不大。尽管我们的研究凸显了至少在所考虑的填充率下获得具有输运平台的 FTI 所面临的挑战——即便在分数 Chern 绝缘体已获实验证实的大角度 tMoTe$_2$ 中也是如此——但我们也提供了潜在的样品工程路径,以提升 FTI 相的稳定性。

英文摘要:

Using comprehensive exact diagonalization calculations on $θ\approx 3.7 ^{\circ}$ twisted bilayer MoTe$_2$ ($t$MoTe$_2$), as well as idealized Landau level models also relevant for lower $θ$, we extract general principles for engineering fractional topological insulators (FTIs) in realistic situations. First, in a Landau level setup at $ν=1/3+1/3$, we investigate what features of the interaction destroy an FTI. For both pseudopotential interactions and realistic screened Coulomb interactions, we find that sufficient suppression of the short-range repulsion is needed for stabilizing an FTI. We then study $θ\approx 3.7 ^{\circ}$ $t$MoTe$_2$ with realistic band-mixing and anisotropic non-local dielectric screening. Our finite-size calculations only find an FTI phase at $ν=-4/3$ in the presence of a significant additional short-range attraction $g$ that acts to counter the Coulomb repulsion at short distances. We discuss how further finite-size drifts, dielectric engineering, Landau level character, and band-mixing effects may reduce the required value of $g$ closer towards the experimentally relevant conditions of $t$MoTe$_2$. Projective calculations into the $n=1$ Landau level, which resembles the second valence band of $θ\simeq 2.1^\circ$ $t$MoTe$_2$, do not yield FTIs for any $g$, suggesting that FTIs at low-angle $t$MoTe$_2$ for $ν=-8/3$ and $-10/3$ may be unlikely. While our study highlights the challenges, at least for the fillings considered, to obtaining an FTI with transport plateaus, even in large-angle $t$MoTe$_2$ where fractional Chern insulators are experimentally established, we also provide potential sample-engineering routes to improve the stability of FTI phases.

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