Measurements of anisotropic mass of magnons confined in a harmonic trap   in superfluid $^3$He-B
  We can pump magnons to a nearly harmonic magneto-textural trap in superfluid $^3$He-B. Using the NMR spectroscopy of levels in the trap we have measured the anisotropic magnon mass and related values of the spin-wave velocities. Based on our measurements we provide values of the Fermi-liquid parameter $F^a_1$. 
V. V. Zavjalov, S. Autti, V. B. Eltsov, P. J. Heikkinen
cond-mat.other