D. T. Sprague

Third sound in3He-4He mixture films

We report third-sound studies of3He-4He mixture films for 0.3≲T≲1.8 K carried out in two different experimental situations. In one experiment detailed measurements of the amplitude of both the temperature and thickness variation of the film were made for pure4He and the results for |ΔT/Δd| are in good agreement with the predictions of Bergman. Mixture studies in this apparatus were made difficult due to the presence of capillary condensation. In spite of this a number of interesting results are reported. Subsequent measurements were made in a new apparatus where capillary condensation effects could be demonstrably avoided. Helium films of 5.7 layers of4He were studied as a function of added amounts of3He. BelowT≃0.7 K the third-sound measurements are consistent with model calculations based on a bilayer film. We conclude that for 0.3≲T≲0.6 K films of the type we have studied are isotopically layered in the van der Waals field provided by the substrate.

3He spin diffusion in thin4He films

Abstract We report measurements of the transverse and longitudinal spin diffusion coefficients for 0.1 – 0.24 monolayers of3He adsorbed on thin3He films as a function of temperature and4He coverage. A strong4He coverage dependence is observed in the spin diffusion which suggests that the3He quasiparticles in the film are strongly scattered by substrate inhomogeneities for4He coverages below 0.5A˚-2.

Spin diffusion and magnetization studies of3He in3He-4He mixture films

The longitudinal spin diffusion coefficient and magnetization of a submonolayer coverage of3He, n3=0.0066 Å−2, in a thin adsorbed4He film has been measured as a function of temperature0.024 K ≤ T≤0.5 K and4He coverage0.21 Å−2≤n4≤0.32 Å−2.

Properties of 3He in thin 4He films

Substantial progress has been made in our understanding of the properties of 3He atoms in thin films of 4He. For such films the 3He occupies discrete quantum states in the film and the system is both rich and complex. Here we discuss progress in this field from several points of view; we briefly discuss early heat capacity and third sound results and concentrate on more recent NMR measurements of the magnetization and relaxation times T1 and T2. Further experimental work and theory for systems of finite 3He coverage is needed to fully understand this fascinating system.

Binding energy of3He in thin4He films

Abstract We report measurements of the magnetization of 0.1 monolayers of 3 He in a thin 4 He film as a function of temperature and from these we determine the binding energies of the 3 He in the mixture film as a function of the 4 He coverage. For 4 He coverages between 0.21 and 0.53A˚ -2 the 3 He binding energies obtained are in reasonable agreement with predictions of Pavloff and Treiner for the 4 He coverage dependence of the binding energy.

Temperature dependence of the NMR relaxation time, T1, of 3He in thin 3He-4He films at various 4He coverages

Abstract The NMR spin-lattice relaxation time, T 1 , of a degenerate submonolayer coverage of 3 He on thin 4 He films has been measured. As a function of the 4 He coverage, T 1 exhibits a maximum, and crosses over to a region with an anomolous temperature dependence at higher coverages.

NMR measurements of 4He in thin 3He4He mixture films

Abstract Evolution of 3He from a 2-d Fermi liquid to bulk-like liquid on thin 3He4He mixture films shows stepped structure in magnetization and NMR relaxation times as a function of 3He coverage d3. Spin-echo measurements in a weakly polarizing field over the temperature range 30