Impurity Effects on the A₁-A₂ Splitting of Superfluid 3He in Aerogel

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When liquid 3He is impregnated into silica aerogel a solid-like layer of 3He atoms coats the silica structure. The surface 3He is in fast exchange with the liquid on NMR timescales. The exchange coupling of liquid 3He quasiparticles with the localized 3He spins modifies the scattering of 3He quasiparticles by the aerogel structure. In a magnetic field the polarization of the solid spins gives rise to a splitting of the scattering cross-section of for `up' vs. `down' spin quasiparticles, relative to the polarization of the solid 3He. We discuss this effect, as well as the effects of non-magnetic scattering, in the context of a possible splitting of the superfluid transition for vs. Cooper pairs for superfluid 3He in aerogel, analogous to the A₁-A₂ splitting in bulk 3He. Comparison with the existing measurements of Tc for B< 5 kG, which show no evidence of an A₁-A₂ splitting, suggests a liquid-solid exchange coupling of order J = 0.1 mK. Measurements at higher fields, B > 20 kG, should saturate the polarization of the solid 3He and reveal the A₁-A₂ splitting.