Kagome金属中双重Van Hove奇性的手征激子序
Chiral excitonic order from twofold van Hove singularities in kagome metals
摘要：
可果美金属AV $_3$ Sb $_5$（A=K，Rb，Cs）的近期实验[M. Kang等人，Nat.Phys.18，301-308（2022）]确定了在费米能附近具有相反方向的双范霍夫奇点（TvHS），产生了两个近似六边形的费米表面--一个是类电子的，另一个是类空穴的。在这里，我们建议，一个TvHS产生一种新的时间反演对称性破缺激子秩序-由于位于相反的埃文霍夫奇点的束缚对电子和空穴而产生。我们引入了一个极小模型的TvHS和调查相互作用引起的多体不稳定性通过微扰重整化群技术和自由能分析。专门为可果美金属AV $_3$ Sb $_5$适当的参数，我们构建了一个相图，包括手性激子，电荷密度波和共存区域。我们提出这是一个解释的AV $_3$ Sb $_5$的实验观察的不同范围。值得注意的是，手性激子态引起量子反常霍尔电导，为可果美金属中观察到的反常霍尔效应提供了一个吸引人的解释。还讨论了双层材料中TvHS机制的可能的替代实现。我们建议，TVHS打开有趣的可能性相关的阶段，丰富的竞争基态，包括激子顺序。
英文摘要：
Recent experiments on kagome metals AV$_3$Sb$_5$ (A=K,Rb,Cs) [M. Kang et al., Nat. Phys. 18, 301-308 (2022)] identify twofold van Hove singularities (TvHS) with opposite concavity near the Fermi energy, generating two approximately hexagonal Fermi surfaces -- one electron-like and the other hole-like. Here we propose that a TvHS generates a novel time-reversal symmetry breaking excitonic order -- arising due to bound pairs of electrons and holes located at opposite concavity van Hove singularities. We introduce a minimal model for the TvHS and investigate interaction induced many-body instabilities via the perturbative renormalisation group technique and a free energy analysis. Specialising to parameters appropriate for the kagome metals AV$_3$Sb$_5$, we construct a phase diagram comprising chiral excitons, charge density wave and a region of coexistence. We propose this as an explanation of a diverse range of experimental observations in AV$_3$Sb$_5$. Notably, the chiral excitonic state gives rise to a quantum anomalous Hall conductance, providing an appealing interpretation of the observed anomalous Hall effect in kagome metals. Possible alternative realisations of the TvHS mechanism in bilayer materials are also discussed. We suggest that TvHS open up interesting possibilities for correlated phases, enriching the set of competing ground states to include excitonic order.
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