Critical and tricritical exponents of 3He-4He solutions from light-scattering data

A light-scattering experiment in 3He-4He mixtures is analysed in the perspective of the 'non-ordering' parameters scaling-laws. The tricritical behaviour is found to be characterized by the specific-heat exponent α = -0.9 +- 0.2 and by the correlation-length exponent ν = 1.15 +- 0.1. These tricritical exponents are renormalized in the manner of Fisher, the corresponding ideal critical exponents being αsup(G) = 0.48 +- 0.1, νsup(G) = 0.6 +- 0.1. The critical behaviour near the lambda-line, at the concentrations x3 = 0.6318 is found to be strongly influenced by its proximity to the tricritical point. The effective renormalized critical exponents are αsup(RI) = -0.36 +- 0.04, νsup(RI) = 0.9 +- 0.06 and the effective ideal critical exponents are αsup(I) = 0.26 +- 0.04, νsup(I) = 0.66 +- 0.08. (author)