Orbital ordering and fluctuations in a kagome superconductor CsV3Sb5

Recently, competing electronic instabilities, including superconductivity and density-wave-like order, have been discovered in vanadium-based kagome metals AV(3)Sb(5) (A = K, Rb, Cs) with a nontrivial band topology. This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state. Here, we performed V-51 and Cs-133 nuclear magnetic resonance (NMR) measurements on a CsV3Sb5 single crystal to clarify the nature of density-wave-like transition in these kagome superconductors. A first-order structural transition is unambiguously revealed below T-s similar to 94 K by observing the sudden splitting of Knight shift in V-51 NMR spectrum. Moreover, combined with Cs-133 NMR spectrum, the present result confirms a three-dimensional structural modulation. By further analyzing the anisotropy of Knight shift and 1/T1T at V-51 nuclei, we proposed that the orbital order is the primary electronic order induced by the first-order structural transition, which is supported by further analysis on electric field gradient at V-51 nuclei. In addition, the evidence for possible orbital fluctuations is also revealed above T-s. The present work sheds light on a rich orbital physics in kagome superconductors AV(3)Sb(5).

Automated summary

This study reveals the nature of density-wave-like transition in vanadium-based kagome superconductors through nuclear magnetic resonance measurements. It confirms the presence of a first-order structural transition and a three-dimensional structural modulation. The study suggests that the orbital order is the primary electronic order induced by the structural transition and provides evidence for possible orbital fluctuations.