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

TL;DR

This study investigates the vortex fluid state in solid helium-4 below an onset temperature T0, revealing velocity-dependent changes in dissipation and NCRIF, and challenging liquid superfluidity explanations for supersolidity.

Contribution

It provides detailed experimental evidence of vortex fluid behavior in solid 4He below T0, with novel velocity and temperature dependence analyses.

Findings

Identification of T0 around 0.5 K where dissipation changes occur

Log(Vac) dependence of NCRIF with temperature-dependent slope

Evidence against liquid superfluidity as the origin of supersolidity

Abstract

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.