SUPERFLUIDITY WITHIN A SMALL HE-4 CLUSTER - THE MICROSCOPIC ANDRONIKASHVILI EXPERIMENT

The infrared spectrum of single oxygen carbon sulfide (OCS) molecules was measured inside large superfluid pure helium-4 droplets and nonsup erfluid pure helium-3 droplets, both consisting of about 10(4) atoms. In the helium-4 droplets, sharp rotational lines were observed, wherea s in helium-3 only a broad peak was found. This difference is interpre ted as evidence that the narrow rotational lines, which imply free rot ations, are a microscopic manifestation of superfluidity. Upon additio n of 60 helium-4 atoms to the pure helium-3 droplets, the same sharp r otational lines were found; it appears that 60 is the minimum number n eeded for superfluidity.