Helium-4 Bose Fluids Formed in One-Dimensional 18 Å Diameter Pores

Bose fluids restricted in one dimension (1D) are realized by adsorbing ${}^4\mathrm{He}$ atoms on the 1D pore walls with a diameter of about 18 Å. The Bose fluid appears above an adsorbed amount after the pore walls are coated with the inert ${}^4\mathrm{He}$ atoms. Heat capacity of the fluid was observed to have a temperature-linear term at low temperatures. This corresponds to the phonon heat capacity of the Bose fluid in the 1D pores. We estimate the phonon velocity and the interaction of the 1D Bose fluid.