摘要：

We report the first measurements of the $Aensuremath{-}B$ phase transition of superfluid ${}^{3}mathrm{He}$ confined within $98%$ silica aerogel in high magnetic fields and low temperatures. A disk of aerogel is attached to a vibrating wire resonator. The resonant frequency yields a measure of the superfluid fraction ${ensuremath{rho}}_{s}/ensuremath{rho}$ of the ${}^{3}mathrm{He}$ within the aerogel. The inferred ${ensuremath{rho}}_{s}/ensuremath{rho}$ value increases substantially at the $A$-to- $B$ transition of the confined superfluid, allowing us to map the $Aensuremath{-}B$ phase diagram as a function of field and temperature. At 4.8 bars, the $Bensuremath{-}T$ transition curve looks very similar to that in bulk with a simple reduction factor of order 0.45 for both transition field and temperature.

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