Critical x-ray scattering at the Peierls transition in the quasi-one-dimensional system

By means of high-resolution x-ray scattering, we have studied the temperature dependence of the critical scattering associated with the Peierls transition in . From a careful intensity and line shape analysis the critical exponents , and were derived. , and are the critical exponents of the temperature dependence of the order parameter, the susceptibility and the correlation length of the order parameter fluctuations, respectively. Though this incommensurate structural phase transition is reported to be continuous, an unusual exponent value is obtained: . The small value of suggests a blurred first-order transition. We also report on the anisotropy of the correlation in the basal plane perpendicular to the -chain direction.