Magnetic susceptibility of the Balian-Werthamer phase of 3He in aerogel

The equilibrium superfluid phase of He-3 impregnated into high porosity (98%) silica aerogels appears to be a non-equal-spin-pairing state in zero field at all pressures, which is generally assumed to be the Balian-Werthamer (BW) phase modified by the depairing effects of the aerogel structure. The nuclear magnetic susceptibility played a key role in identifying the B-phase of pure He-3 with the BW state. We report theoretical calculations of the nuclear magnetic susceptibility for the BW model of superfluid He-3 in aerogel within the framework of the Fermi-liquid theory of superfluid He-3. Scattering of quasiparticles by the aerogel, in addition to Fermi-liquid exchange corrections, leads to substantial changes in the susceptibility of the BW phase. The increase in the magnetic susceptibility of He-3-aerogel compared to pure He-3-B is related to the polarizability of the gapless excitations and the impurity-induced local field. The limited data that is available is in rough agreement with theoretical predictions. Future measurements could prove important for a more definitive identification of the ordered phase, as well as for refining the theoretical model for the effects of disorder and scattering on the properties of superfluid He-3.