AV₃Sb₅ (A = K, Rb, Cs) 中的双基本能带表示模型、费米面嵌套与表面拓扑超导
Two elementary band representation model, Fermi surface nesting, and surface topological superconductivity in $A$V$_{3}$Sb$_ {5}$ ($A = \text{K, Rb, Cs}$)
AI总结：
本文通过构建双基本能带表示模型刻画 AV₃Sb₅ 的能带拓扑，发现费米面嵌套与 2×2×2 电荷密度波重构一致，并在 (001) 表面获得非平庸超导能隙，为研究 Majorana 物理提供了新平台。
摘要：
最近发现的钒基 Kagome 金属 AV₃Sb₅ (A = K, Rb, Cs) 因电荷密度波（CDW）序、能带拓扑和超导电性之间的相互作用而备受关注。本文通过识别基本能带表示（EBRs），构建了一个双 EBR 的石墨烯-Kagome 模型，以刻画这些 Kagome 金属中两个低能范霍夫奇点色散，以及更重要的非平庸能带拓扑。该模型由 A_g@3g（V-d_{x²−y²/z²}，Kagome 位点）和 A₂″@2d EBRs（Sb1-p_z，蜂窝位点）组成。我们通过计算电子磁化率 χ(q) 研究了费米面不稳定性。在三个 L 点处获得了显著的费米面嵌套峰，其中嵌套矢量的 z 分量与 M–L 方向上的反交叉点表现出密切关系。L 点处的嵌套峰与这些化合物中 2×2×2 的 CDW 重构一致。此外，还计算了子晶格分辨的裸磁化率，并在 L 点处观察到类似的尖锐峰，表明存在强反铁磁涨落。假设体态 s 波超导配对，在 (001) 表面上获得了螺旋表面态和非平庸超导能隙。与 FeTe₁₋ₓSeₓ 超导体类似，我们的结果确立了另一种具有非平庸能带拓扑的化学计量比超导体的材料实现，为研究凝聚态物质中奇异的 Majorana 物理提供了一个有前景的平台。
英文摘要：
The recently discovered vanadium-based Kagome metals $A$V$_{3}$Sb$_{5}$ ($A = \text{K, Rb, Cs}$) are of great interest with the interplay of charge density wave (CDW) order, band topology and superconductivity. In this paper, by identifying elementary band representations (EBRs), we construct a two-EBR graphene-Kagome model to capture the two low-energy van-Hove-singularity dispersions and, more importantly, the nontrivial band topology in these Kagome metals. This model consists of $A_g@3g$ (V-$d_{x^2-y^2/z^2}$, Kagome sites) and $A_2''@2d$ EBRs (Sb1-$p_z$, honeycomb sites). We have investigated the Fermi surface instability by calculating the electronic susceptibility $χ(\mathbf{q})$. Prominent Fermi-surface nesting peaks are obtained at three L points, where the $z$ component of the nesting vector shows intimate relationship with the anticrossing point along M--L. The nesting peaks at L are consistent with the $2\times 2\times 2$ CDW reconstruction in these compounds. In addition, the sublattice-resolved bare susceptibility is calculated and similar sharp peaks are observed at the L points, indicating a strong antiferromagnetic fluctuation. Assuming a bulk $s$-wave superconducting pairing, helical surface states and nontrivial superconducting gap are obtained on the (001) surface. In analogous to FeTe$_{1-x}$Se$_{x}$ superconductor, our results establish another material realization of a stoichiometric superconductor with nontrivial band topology, providing a promising platform for studying exotic Majorana physics in condensed matter
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