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.