上海科技大学知识管理系统

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 .