Charge density wave and fluctuations in KV₃Sb₅ kagome superconductor studied by V K-edge X-ray absorption spectroscopy

The local structure of the KV₃Sb₅ kagome superconductor has been studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure (EXAFS) analysis reveals significant temperature-dependent changes in the local environment around vanadium (V) atoms. Notably, the V-Sb bond distance exhibits a distinct alteration in thermal expansion behavior at temperatures far exceeding the charge density wave (CDW) transition temperature (∼78 K). Additionally, mean square relative displacements of V-V pairs show excess distortions across the CDW transition, suggesting direct coupling between the CDW and local lattice distortions. X-ray absorption near-edge structure (XANES) measurements further demonstrate an unusual electronic response, providing evidence of a fluctuating CDW state. These findings highlight the complex interplay between structural and electronic degrees of freedom in KV₃Sb₅. The results advance our understanding of local structural dynamics during CDW formation in kagome materials and offer critical insights into the mechanisms driving quantum phases in these systems.