Orientation-Dependent Nuclear Magnetic Resonance (NMR) Studies of Charge Orders in Kagome Superconductors

AV₃Sb₅ (A=K, Rb, Cs) kagome lattices exhibit both a non-conventional charge density wave (CDW) order (TCDW ∼ 80 − 104 K) and a topological superconducting ground state (TC ∼ 0.9 − 2.5 K).^1-7 The CDW state may serve as a precursor to superconductivity, as they can both arise from the same electronic interactions. Consequently, the elucidation of the CDW mechanism in kagome metals assumes significant importance in unraveling the underlying fundamental mechanisms governing their unconventional superconductivity. We employed orientation-dependent ⁵¹V single crystal nuclear magnetic resonance (NMR) experiments on to investigate the superstructural deformation of the crystal lattice associated with CDW in A=Cs variant. This analysis involves the derivation of anisotropic Knight shift (K) and electric field gradient (EFG) tensors, both highly sensitive to structural transitions and modulations of the electronic charge density caused by CDW. Our examination of the temperature-dependent evolution of K and EFG tensors for ⁵¹V reveals particular modes of structural distortion occurring below CDW transition consistent with synchrotron x-ray diffraction and is in accordance with theoretical calculations. Other indications regarding the charge inhomogeneity associated with charge orders in kagome lattices will be discussed.

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