  Vacancies are prevalent and versatile in solid-state physics and materials
science. The role of vacancies in strongly correlated materials, however,
remains uncultivated until now. Here, we report the discovery of an
unprecedented vacancy state forming an extended buckled-honeycomb-vacancy (BHV)
ordering in Ir$_{16}$Sb$_{18}$. Superconductivity emerges by suppressing the
BHV ordering through squeezing of extra Ir atoms into the vacancies or
isovalent Rh substitution. The phase diagram on vacancy ordering reveals the
superconductivity competes with the BHV ordering. Further theoretical
calculations suggest that this ordering originates from a synergistic effect of
the vacancy formation energy and Fermi surface nesting with a wave vector of
(1/3, 1/3, 0). The buckled structure breaks the crystal inversion symmetry and
can mostly suppress the density of states near the Fermi level. The
peculiarities of BHV ordering highlight the importance of "correlated
vacancies" and may serve as a paradigm for exploring other non-trivial
excitations and quantum criticality.
