摘要：

The phase diagram of the superfluid phases of $^{3}$He in 98% aerogel wasdetermined in the range of pressure from 15 to 33 bars and for fields up to 3kG using high-frequency sound. The superfluid transition in aerogel at 33.4bars is field independent from 0 to 5 kG and shows no evidence of an$A_{1}-A_{2}$ splitting. The first-order transition between the A and B-phasesis suppressed by a magnetic field, and exhibits strong supercooling at highpressures. We show that the equilibrium phase in zero applied field is theB-phase with at most a region of A-phase {\small $\alt$} 20 $\mu$K just belowT${_c}$ at a pressure of 33.4 bars. This is in contrast to pure $^{3}$He whichhas a large stable region of A-phase and a polycritical point. The quadraticcoefficient for magnetic field suppression of the AB-transition,$g_{a}(\beta)$, was obtained. The pressure dependence of $g_{a}(\beta)$ ismarkedly different from that for the pure superfluid, $g_{0}(\beta)$, whichdiverges at a polycritical pressure of 21 bars. We compare our results withcalculations from the homogeneous scattering model for $g_{a}(\beta)$, definedin a Ginzburg-Landau theory in terms of strong-coupling parameters $\beta$. Wefind qualitatively good agreement with the experiment if the strong-couplingcorrections are rescaled from known values of the $\beta$'s for pure $^{3}$He,reduced by the suppression of the superfluid transition temperature. Thecalculations indicate that the polycritical pressure in the aerogel system isdisplaced well above the melting pressure and out of experimental reach. Wecannot account for the puzzling supercooling of the aerogel AB-transition inzero applied field within the framework of known nucleation scenarios.

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