Ow-dimensional helium quantum fluids realized under nano-extreme conditions

The ⁴He and ³He quantum fluids in various dimensions and with interactions different from those of the bulk fluids have been realized under the new extreme conditions constituted in nanopores. The 4He fluid films adsorbed in one-dimensional (ID) nanopores form nano-quantum fluid. The 4He films formed in ID and 3D nanopores manifest ID and 3D phonon states, respectively, at sufficiently low temperatures. Their superfluid onsets show an obvious dependence on the pore connectivity. The 2D Kosterlitz-Thouless superfluid transition was studied at extremely high frequencies where the vortex diffusion length in a period is as small as the core diameter. In the ID and 3D nanopores preplated with ⁴He films, the ³He gases at dilute densities show dimensional crossovers from the 2D Boltzmann gas to the ID and 3D gas states, respectively, with decreasing temperature. The degenerate states of 3He in nanopores are expected to depend on the dimensionality and the interactions, which are different from those of the bulk liquids. Zero-dimensional fluids, i.e., quantum clusters, are likely to be realized in nanocages of the Y-type zeolite.