³He Fluid Formed in One‐Dimensional 1.8 nm Pores Preplated with ⁴He Layer

In one‐dimensional (1D) nanopores 1.8 nm in diameter preplated with 1.2 atomic layers of ⁴He, we have made ³He film tubes whose diameter is estimated to be about 1.0 nm. At a low ³He density, the heat capacity shows that of a 2D Boltzmann gas at high temperatures followed by a Schottky‐like peak at about 300 mK. This result can be understood in terms of dimensional crossover from 2D to 1D with decreasing temperature. The peak appears at a temperature about 0.3 times the energy gap between the ground state and the first excited states of the azimuthal motion in the ³He fluid tubes.