The smectic-$A$ phase of a liquid crystal is characterized by a one-dimensional mass density wave in a three-dimensional liquid. High-resolution x ray measurements in the smectic-$A$ phase of octyloxycyanobenzylidene (8OCB) show that the order-parameter scattering does not exhibit normal Bragg line profiles but rather corresponds to a power-law singularity of the form ${(q_{\parallel }-q_0)}^{-2\mathrm{}}$, with $q_{\parallel }$ being the longitudinal wave-vector component. Also, the transverse line profile is anomalous.

• Received 20 June 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.1668