Nuclear Magnetic Resonance Studies of the Formation and Dynamics of Charge Ordering in ScV₆Sn₆

ScV₆Sn₆ exhibits a distinct CDW transition¹ with unique features. Unlike in superconducting AV₃Sb₅ (A=K, Rb, Cs), the CDW in ScV₆Sn₆ originates primarily from an extremely flat phonon mode² involving out-of-plane Sn vibrations^3,4. This leads to significant changes in the Sn-derived bands, with more subtle effects on the V-derived kagome bands. These distinct features of the ScV₆Sn₆ CDW provide a unique opportunity to study CDW formation mechanisms that differ from those in the AV₃Sb₅ family. We employed orientation-dependent ⁴⁵Sc nuclear magnetic resonance (NMR) experiments to uncover the roles of electronic correlations and lattice degrees of freedom in ScV₆Sn₆ and investigate the formation, dimensionality, and dynamics of its CDW. Our examination of the temperature evolution of orientation-dependent NMR parameters reveals charge density modulation along specific crystal axes associated with the charge-ordering transition in kagome metals. The charge modulation fluctuation detected by NMR arises from a rattling motion of Sc-Sn-Sn chains within compressible Sc-Sn-Sn columns, originating from the unique crystal structure of ScV₆Sn₆³. The slow charge density fluctuation reflects competing charge orders with wave vectors q=(1/3,1/3,1/3) and q=(1/3,1/3,1/2) across the phase transition⁴. The implications of these phenomena are discussed in relation to charge ordering in related systems where NMR reveals similar slow charge fluctuations and spatial inhomogeneity.



References: 1. Phys. Rev. Lett. 129, 216402 (2022). 2. Nat. Commun. 14, 6646 (2023). 3. J. Am. Chem. Soc.145 (38) 20943 (2023). 4. Phys. Rev. Mater. 7, 104201 (2023).