3He transverse excited state occupation in thin 3He-4He films

The discovery that He-3 was occupying transverse excited states at submonolayer coverages in He-3-He-4 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 groundstate 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 He-3 occupation of the first excited state at submonolayer coverages. The mechanism is a model He-3-He-3 effective interaction due to one ripplon exchange. This effective interaction is density dependent and very long ranged. It strongly modifies the small-le properties of the He-3 self-energy and, in particular, causes the ground-state to first excited state level spacing to decrease with increasing He-3 areal density.