Interpretation of experimental data near λ-transition point in liquid helium

The recently published experimental data for specific heat C p of liquid helium in zero gravity conditions very close to the λ–transition have been discussed. We have shown that these data allow different interpretations. They can be well interpreted within the perturbative RG approach and within our recently developed theory, as well. Allowing the logarithmic correction, the corresponding fits lie almost on top of each other over the whole range of the reduced temperatures t (for bin averaged data) 6.3 ×10 -10 > t > 8.8 ×10 -3 . However, the plot of the effective exponent α eff (t) suggests that the behaviour of C p , probably, changes very close to T λ . To clarify this question, we need more accurate data for t>10 -7 . In addition, we show that the experimental data for superfluid fraction of liquid helium close to T λ within t ∈[3 ×10 -7 ;10 -4 ] can be better fit by our exponents ν=9/13 ≃0.6923, Δ=5/13 ≃0.3846 than by the RG exponents ν≃0.6705 and Δ≃0.5. The latter ones are preferable to fit the whole measured range t ∈[3 ×10 -7 ;10 -2 ] where, however, remarkable systematic deviations appear. Our estimated value 0.694 ±0.017 of the asymptotic exponent ν well agrees with the theoretical prediction ν=9/13. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005