title: Ac vortex-dependent torsional oscillation response and onset temperature T0 in solid 4He.
abstract: Detailed studies of ac velocity V_{ac} and T dependence of torsional oscillator responses of solid 4He are reported. A characteristic onset temperature T_{0} approximately 0.5 K is found, below which a significant V_{ac}-dependent change occurs in the energy dissipation for the samples at approximately 32 bar and for one at 49 bar. A V_{ac} dependence of the so-called "nonclassical rotational inertia" fraction also appears below approximately T_{0}. The log(V_{ac}) linear dependence, which suggests involvement of quantized vorticies, was examined in the nonclassical rotational inertia fraction. We find a common 1/T;{2} dependence for this linear slope change in all of the samples for 30<V_{ac}<300 microm/s. We discuss that our observation is consistent with nonlinear rotational susceptibility of the vortex fluid, proposed by Anderson above T_{c} below T0.
authors.affiliation: Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwanoha 5-1-5, Kashiwa 277-8581, Japan.
authors.forename: Andrey
authors.initials: A
authors.lastname: Penzev
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Yasuta
authors.forename: Minoru
authors.initials: M
authors.lastname: Kubota