The kagome material CsTi3Bi5, which is isostructural to the extensively studied charge density wave (CDW) compound CsV3Sb5, 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 CsTi3Bi5 to investigate its electronic properties comprehensively. It is found that the overall optical spectra are very similar to those of CsV3Sb5, but the existence of CDW instability is ruled out in CsTi3Bi5. Via careful comparison to the optical responses of CsV3Sb5, we attribute this difference to a significant reduction in the itinerant carrier density of CsTi3Bi5, 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 CsV3Sb5 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 CsTi3Bi5. Our findings contribute to a deeper understanding of exotic phenomena in CsTi3Bi5 and provide valuable insights into the role of van Hove singularity in CsV3Sb5.
@article{arxiv.2409.03688,
title = {Infrared spectroscopy study of kagome material CsTi$_3$Bi$_5$},
author = {Liye Cao and Xiangqi Liu and Jiayi Cheng and Bixia Gao and Xiaoting Zhang and Yanfeng Guo and Fengjie Ma and Rongyan Chen},
journal= {arXiv preprint arXiv:2409.03688},
year = {2025}
}