Layered 4He in Hectorite: A New Quasi-Two-Dimensional Environment for Quantum Liquids

We have studied the properties of quasi-two-dimensional ⁴He in an environment provided by the layered structure of hectorite. A phase transition occurs for areal densities between n=0.029 Å^–2 and n=0.032 Å^–2 where the structure of ⁴He changes abruptly from a 4-layer to a 5-layer configuration. The signatures of this phase transition are detectable in the static density–density response function and in the density–dependence of the roton minimum.