α-particle condensate states in 16O

The existence of a rotational band with the α+C12(02+) cluster structure, in which three α particles in 12C(02+) are locally condensed, is demonstrated near the four-α threshold of 16O in agreement with experiment. This is achieved by studying structure and scattering for the α+C12(02+) system in a unified way. A drastic reduction (quenching) of the moment of the inertia of the 0+ state at 15.1 MeV just above the four-α threshold in 16O suggests that it could be a candidate for the superfluid state in α-particle condensation.