3He Transverse Excited State Occupation in Thin 3He-4He Films

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The discovery that 3He was occupying transverse excited states at submonolayer coverages in 3He-4He mixture films on a Nuclepore substrate, was a surprise. In this note we discuss the relationship between theory and experiment in attempting to understand the physics of this behavior. We first discuss various single-atom-limit calculations of the level spacing between the ground-state and first excited state. We then introduce a free, quasi-particle picture for analyzing experimental magnetization step data and compare those results with the single-atom-limit calculations. The experiments clearly show excited state occupation at submonolayer coverages in contradistinction with the calculations. We then briefly discuss a microscopic, semi-phenomenological theory which, in agreement with experiment, yields 3He occupation of the first excited state at submonolayer coverages. The mechanism is a model 3He-3He effective interaction due to one ripplon exchange. This effective interaction is density dependent and very long ranged. It strongly modifies the small-k properties of the 3He self-energy and, in particular, causes the ground-state to first excited state level spacing to decrease with increasing 3He areal density.

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