Abstract
We report a detailed synchrotron x-ray-scattering study of the structural fluctuations near the spin-Peierls transition in CuGe. Below the transition temperature , the superlattice peak profile is resolution limited and the peak intensity, which is proportional to the order parameter squared, is well described by a simple power law, . The fitted value of , 0.33(3), agrees quantitatively with previously reported results from neutron-diffraction measurements. Above the transition temperature , pretransitional lattice fluctuations are observed within about 1 K above . The length scale of these fluctuations is about an order of magnitude larger than that characterizing the bulk critical fluctuations. The line shape of these large length-scale fluctuations is consistent with a Lorentzian-squared form. The measured critical exponents associated with the large length-scale fluctuations are , and . Similar large length-scale fluctuations have been observed at the structural transitions in some perovskites and the magnetic transitions in holmium and terbium. We suggest that in CuGe the large length-scale fluctuations reflect the disconnected susceptibility originating from random field Ising-type local defects.
- Received 23 August 1995
DOI:https://doi.org/10.1103/PhysRevB.52.15420
©1995 American Physical Society