Superfluid Onset of $$^{4}$$ He Nanotube Depending on a One-Dimensional Length.

A 1D Bose fluid has been actually realized for the $$^{4} $$ He nanotubes formed in 1D nanochannels, and the superfluidity observed by a torsional oscillator. Dependence of the superfluid density on the channel diameter was qualitatively well explained by a theory that the superfluid onset temperature depends on an effective 1D length $$L_{\mathrm {eff}}$$ which is the ratio of the length to the circumference of the fluid nanotube. To examine this mechanism, we measured the superfluid of a new $$ ^{4} $$ He nanotube formed in the 1D channel with the diameter 3.1 nm and the length 10-20 $$\upmu $$ m, which is one order longer than that of the former channels. The observed superfluid is similar to that of the much smaller diameter, typically 2.2 or 1.8 nm, channel with the shorter length. This indicates that the superfluid onset observed for the present $$^{4}$$ He nanotubes is determined by the finite effective 1D length $$L_{\mathrm {eff}}$$ , not by the channel diameter. In addition to this length dependence, dynamics at the 1D superfluid onset is indicated by a dissipation peak at $$ 10^{3}$$ Hz measurement frequency. [ABSTRACT FROM AUTHOR]