CRITICAL-BEHAVIOR AT NEMATIC SMECTIC-A(1) PHASE-TRANSITIONS .2. PREASYMPTOTIC 3-DIMENSIONAL XY ANALYSIS OF X-RAY AND CP DATA

X-ray data are reported for the nematic phase near the nematic (N)-sme ctic-A1(Sm-A1) transition in a binary mixture of pentylphenylcyanobenz oyloxy benzoate (DB5CN) + cyanobenzoyloxypentylstilbene (C5 stilbene). These data and x-ray data from four other N-Sm-A1 systems, plus the c orresponding high-resolution C(p) data, are analyzed using the exact s olutions of preasymptotic three-dimensional (3D) XY theory. The correl ation volume xi(parallel-to)xi(perpendicular-to)2, smectic susceptibil ity sigma, and heat capacity C(p) are in good agreement with preasympt otic theoretical predictions. First-order corrections-to-scaling terms were known previously to be important for describing C(p); their impo rtance for xi(parallel-to)xi(perpendicular-to)2 and sigma is demonstra ted here. Many universal features of the 3D XY model are confirmed by the present self-consistent analysis, but the critical anisotropy of t he individual lengths xi(parallel-to) and xi(perpendicular-to) and the fact that C(p) exhibits a normal XY amplitude ratio rather than the t heoretically predicted inverted ratio are still unresolved issues.