Dimensional crossover and reentrant superconductivity in pressurized kagome metals AV3Sb5

Non-magnetic kagome metals, AV₃Sb₅ (A: K, Rb, Cs), offer a new promising platform for engineering topological and correlated electrons [1,2]. At ambient pressure, these compounds show a competition between an exotic charge-density wave and superconductivity that are rooted in an intricate interplay of topologically non-trivial Dirac fermions, localized flat-band electrons, and van Hove singularities in the vicinity of the Fermi level. These features can be traced back to the effectively 2D band structure of vanadium kagome planes. We pioneered the broadband optical studies of AV₃Sb₅ and identified a significant damping of charge carriers [3, 4, 5], potentially related to electron-phonon coupling that has immediate implications for superconductivity.

The tunability of these properties with external means opens interesting new directions in the research of kagome metals. For example, an unusual reentrant superconductivity of AV₃Sb₅ was observed in transport measurements under pressure. In this presentation, I will summarize pressure evolution of AV₃Sb₅ revealed by single-crystal XRD, high-pressure infrared spectroscopy, and density-functional calculations. This combination of experimental and computational techniques allows a simultaneous probe of crystal and electronic structures under both hydrostatic and non-hydrostatic conditions. We show that, despite the initial similarity of AV₃Sb₅ with different alkaline metals (A = K, Rb, Cs) at ambient pressure, these compounds show a different sequence of pressure-induced structural phase transitions, which further depend on the extent of non-hydrostaticity of the pressure environment [6, 7].

Electronic structure calculated using experimental atomic positions and also probed directly by infrared spectroscopy reveals a dimensional crossover caused by the formation of interlayer Sb-Sb bonds [7]. The strongly 2D structures of AV₃Sb₅ become essentially 3D at elevated pressures. These changes lead to a reconstruction of the Fermi surface that clearly correlates with the reentrant behavior of superconductivity. We further reveal the interplay between topological and localized carriers that follow the evolution of the Fermi surface.

Our study demonstrates pressure-induced dimensional crossover as an important tool for tailoring novel electronic materials, such as kagome metals. Concurrently, we show that their high-pressure phases intimately depend on the pressure environment and its deviation from hydrostaticity.

[1] B. R. Ortiz et al., Phys. Rev. Materials 3, 094407 (2019)
[2] H. Luo et al., Nature Communications 13, 273 (2022)
[3] E. Uykur et al., Phys. Rev. B 104, 045130 (2021)
[4] E. Uykur et al., npj Quantum Materials 7, 16 (2022)
[5] M. Wenzel et al. Phys. Rev. B 105, 245123 (2022)
[6] A. A. Tsirlin et al. SciPost Physics 12, 049 (2022)
[7] A. A. Tsirlin et al. arXiv: 2209.02794