Vortex Fluid State below an Onset Temperature T_0 of Solid 4He

Detailed studies of AC velocity Vac and temperature dependence of torsional oscillator responses of solid 4He are reported. A characteristic onset temperature T0 about 0.5 K is found, below which a significant Vac dependent change occurs in the energy dissipation for the sample at 32 bar. A Vac dependence of the non-classical rotational inertia fraction, NCRIF also appears below about T0. This value of T0 excludes the possible explanation of supersolid by liquid superfluidity in grain boundaries or other liquid related origins. The log(Vac) linear dependence was found in NCRIF. Furthermore, this linear slope changes in proportion to 1/T 2 for 40 < Vac < 400 micro-m/s, then crosses over to about 1/T for larger Vac. We discuss properties of the vortex fluid state proposed by Anderson above Tc, below T0.Comment: 4pages,4 figure

Annealing Effect for Supersolid Fraction in 4^4He

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 $\mu$m/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.Comment: to be published in J. of Low Temp. Phys. (QFS2006 proceedings