Surface coupling to collective and single-particle spin modes in normal ³He

We propose a simple technique for probing the single-particle and collective excitations in normal ³He via a standing magnetic surface wave of arbitrary Ω and fixed k generated by a meander-line coil. An analytic treatment of the Landau-Sillin equation enables us to calculate the power absorption spectrum, which displays singularities associated with the l = 0 spin mode and a Doppler-shifted spin resonance (DSSR) of the single-particle excitations. Experimental measurement of the spectrum would determine the Landau parameters (F₀^a, F₁^a) with spectroscopic precision. Furthermore, observation of the DSSR thresholds would provide an independent determination of the Fermi velocity Ν and F₀^a. Finally, a possibility of exciting higher, l ≥ 1, spin modes is briefly mentioned in the framework of an extended Leggett-Rice equation.