Nuclear Magnetic Resonance Investigation of 3He Surface States in Adsorbed 3He-4He Films
We have made nuclear susceptibility measurements of 3He atoms adsorbed on the free surface of a 4He film. Apart from providing a unique opportunity for studying the magnetic properties of a two-dimensional Fermi system, this experiment is of interest in relation to recent theoretical and experimental investigations of “surface states” in 3He-4He mixtures.1–3 Specific heat measurements2 carried out with a Vycor substrate similar to that used in this work have shown that there is a strong dependence on whether or not a free surface is present. With a free surface the specific heat rises almost linearly as expected for a degenerate Fermi gas, while at full pores the limiting low-temperature specific heat is independent of temperature, indicating that the 3He atoms are behaving as a nondegenerate gas. The latest surface tension data3 have confirmed Andreev’s predictions1 that 3He atoms are bound on the free 4He surface with a binding energy ε o equal to 1.8°K and that if the surface concentration is sufficiently dilute, they constitute a two-dimensional gas of quasiparticles with effective mass m* = 1.7m 3, where m 3 is the bare 3He mass. For higher surface densities, however, there appears to be an attractive interaction V 0 between the surface quasiparticles, and Guo et al.3 estimate that this alters the chemical potential by approximately -0.7°K for a complete layer.
KeywordsSpecific Heat Measurements2 Nuclear Magnetic Resonance Investigation High Surface Density Porous Vycor Glass Degeneracy Temperature
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