Two experimental tests of the Halperin-Lubensky-Ma effect at the nematic-smectic-A phase transition

We have conducted two quantitative tests of predictions based on the Halper in-Lubensky-Ma (HLM) theory of fluctuation-induced first-order phase transi tions. First, we explore the effect of an external magnetic field on the ne matic-smectic-A transition in a liquid crystal. Second, we examine the depe ndence of the first-order discontinuity; as a function of mixture concentra tion in pure 8CB and three 8CB-10CB mixtures. We find the first quantitativ e evidence for deviations from the HLM theory.