THERMAL-EXPANSION COEFFICIENT NEAR THE SUPERFLUID TRANSITION OF HE-4 IN AN AEROGEL

We measured the isobaric thermal expansion coefficient beta(P) near the superfluid transition of He-4 in an aerogel along six isobars between 3 and 24 bars. The data yield the specific-heat exponents-alpha and alpha' and amplitude ratio A/A'. Fits by power laws in t=T/T(c)-1, where T(c) is the transition temperature, produced alpha congruent-to -0.6 and alpha' congruent-to -1.0 not-equal alpha. Including an analytic background axt permitted alpha=alpha' congruent-to -0.59, but required a very large coefficient a and yielded A'/A congruent-to 0. The exponents are inconsistent with that of rho(s) and hyperscaling in three dimensions.