We present a detailed discussion of the crossover from mean-field to Ising critical behavior upon approach of the critical point, both for ${}^3\mathrm{He}$ and Xe. By combining different sets of experimental data, we are able to cover an unusually large temperature range on either side of the critical temperature $T_c.$ Below $T_c,$ we thus can make an accurate comparison with a recent calculation for the crossover of the coexistence curve. For the regime above $T_c,$ an analysis of the compressibility demonstrates that the crossover regime in ${}^3\mathrm{He}$ is unexpectedly widened by a subtle interplay between quantum and critical fluctuations.

• Received 25 January 2000

DOI:https://doi.org/10.1103/PhysRevE.62.3257