Infrared spectroscopy study of kagome material CsTi${}_3$Bi${}_5$

Abstract

The kagome material CsTi${}_3$Bi${}_5$, which is isostructural to the extensively studied charge density wave (CDW) compound CsV${}_3$Sb${}_5$, exhibits intriguing electronic features within its two-dimensional kagome lattices of titanium atoms. Here, we perform optical spectroscopic measurements together with the first-principles calculations on single-crystalline CsTi${}_3$Bi${}_5$ to investigate its electronic properties comprehensively. It is found that the overall optical spectra are very similar to those of CsV${}_3$Sb${}_5$, but the existence of CDW instability is ruled out in CsTi${}_3$Bi${}_5$. Via careful comparison to the optical responses of CsV${}_3$Sb${}_5$, we attribute this difference to a significant reduction in the itinerant carrier density of CsTi${}_3$Bi${}_5$, which is associated with the absence of van Hove singularity near the Fermi level at $M$ point. This result supports the scenario that the CDW in CsV${}_3$Sb${}_5$ is driven by the nesting of van Hove singularity. Additionally, we unveil some exotic low-lying absorption features, which provide clear evidence of flat bands in CsTi${}_3$Bi${}_5$. Our findings contribute to a deeper understanding of exotic phenomena in CsTi${}_3$Bi${}_5$ and provide valuable insights into the role of van Hove singularity in CsV${}_3$Sb${}_5$.

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Cited by in corpus (3)

• Kagome metals
• Topological electronic structure and electronic nematicity in candidate kagome superconductors, ATi${}_3$Bi${}_5$ (A = Rb, Cs)
• Interplay of $d$- and $p$-states in RbTi${}_3$Bi${}_5$ and CsTi${}_3$Bi${}_5$ flat-band kagome metals