Helium-4 and helium-3/helium-4 mixture films on Nuclepore and hydrogen
This work extends the study of helium films with the description of two experiments performed on different substrates. The primary experiment involves 4He and 3He-4He mixture films on a solid H2 substrate. The secondary experiment is concerned with the behavior of mixture films on Nuclepore.
The substrate for the helium-on-hydrogen experiment was chosen for the weak binding potential for helium on hydrogen. Unlike most substrates, H 2 will support a superfluid 4He film less dense than a single bulk-density atomic layer. In recent years, interesting effects have been observed for helium-on-hydrogen systems.
The H2 experiment is presented with the results of quartz crystal microbalance measurements and attempted third sound measurements. The quartz crystal microbalance technique measures mass coupling and reveals several interesting features in monolayer and submonolayer helium films on H2. Submonolayer superfluidity and possible phase separation of two-dimensional submonolayer 4He films on solid H2 is reported. 3He–4He mixture films on the H2 substrate reveal novel dependence of the Kosterlitz-Thouless transition temperature on 3He coverage and an unexpected feature at lower temperature.
Third sound resonance and NMR measurements are reported for the Nuclepore experiment. The Nuclepore experiment is the continuation of a long-term study of multilayer 3He-4He mixture films. NMR relaxation times, magnetization, and spin diffusion measurements are discussed over a range of temperatures and mixture film coverages. Third sound measurements taken at the same mixture film coverages reveal interesting structure as a function of temperature. Third sound frequency data at temperatures near 150 mK and at 3He coverages greater than one atomic layer exhibit a local maximum that responds to changes in both 3He and 4He coverage.