We report the inelastic X-ray scattering (IXS) experimental results of iridium oxide Ca 5 Ir 3 O 12 with a strong spin-orbit interaction, showing the hidden order at 105 K where no superlattice reflections were observed so far. We measured the IXS spectra of Ca 5 Ir 3 O 12 along Γ-A, Γ-M, Γ-K-M, M-L, and K-H directions in the Brillouin zone of a hexagonal lattice down to 20 K. The obtained phonon spectra show almost no change on cooling; there are no soft phonon modes. However, the superlattice reflections specified by wavevector q=(1/3, 1/3, 1/3) are observed below 105 K. For the order parameter
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.