Annealing Effect for Supersolid Fraction in 4He

We report on experimental confirmation of the non-classical rotational inertia (NCRI) in solid helium samples originally reported by Kim and Chan. The onset of NCRI was observed at temperatures below ≈400 mK. The ac velocity for initiation of the NCRI suppression is estimated to be ≈10 μm/sec. After an additional annealing of the sample at T=1.8 K for 12 hours, ∼10% relative increase of NCRI fraction was observed. Then after repeated annealing with the same conditions, the NCRI fraction was saturated. It differs from Reppy’s observation on a low pressure solid sample.