Tri-hexagonal charge order in kagome metal CsV₃Sb₅ revealed by ¹²¹Sb nuclear quadrupole resonance

We report 121Sb nuclear quadrupole resonance (NQR) measurements on kagome superconductor CsV3Sb5 with T c = 2.5 K. 121Sb NQR spectra split after a charge density wave (CDW) transition at 94 K, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition. The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers, which is consistent with 2 × 2 × 2 superlattice modulation. The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.