Universality of static properties near the superfluid transition inHe4

Abstract

We present the results of new analyses of static properties near the superfluid transition in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ which incorporate recent accurate entropy measurements. They yield a superfluid density exponent $\zeta =0.6717\mathrm{}\pm 0.0004$ at vapor pressure, where the quoted error is 1 standard deviation. This yields a specific-heat exponent $\alpha =-0.015\mathrm{}$ via scaling. We assumed these exponents to be universal (i.e., independent of pressure) in the remainder of the analysis. Their systematic errors are difficult to estimate; therefore we analyzed data at higher pressures with the three values $\zeta =0.669, 0.672, \mathrm{and} 0.675$, corresponding to $\alpha =-0.007, -0.016, \mathrm{and} -0.025\mathrm{}$, respectively, which surely bracket the true values. Regardless of the exponent pair used, pressure-independent results were obtained for all experimentally accessible amplitude combinations that have been predicted to be universal. Specifically, the problem of apparent deviations from two-scale-factor universality along the $\lambda$ line has been resolved by the use of the new entropy measurements and this analysis.