High-Resolution X-Ray Study of a Second-Order Nematic—Smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>Phase Transition

Abstract

We have carried out a high-resolution x-ray-scattering study of the critical fluctuations in the nematic phase associated with the nematic-smectic-$A$ transition in N-$p$-cyanobenzylidene-$p$-octyloxyanilene (CBOOA). It is shown that for $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\ensuremath{\lesssim}\frac{T}{{T}_{c}}\ensuremath{-}1\ensuremath{\lesssim}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ the transverse and longitudinal correlation lengths diverge with identical exponents, that is, $|{\ensuremath{\nu}}_{L}\ensuremath{-}{\ensuremath{\nu}}_{T}|&lt;0.03$. As one approaches ${T}_{c}$ the system appears to crossover from helium- to mean-field critical behavior at a reduced temperature of \ensuremath{\sim}${10}^{\ensuremath{-}3}$.