Critical Phenomena of the Spin-Peierls Transition in CuGe O₃

We have studied the critical phenomena associated with the spin-Peierls transition which occurs in the inorganic compound CuGeO3 by means of x-ray scattering. Our observation of the temperature dependence of the superlattice reflection arising from the dimerization of the lattice shows that the asymptotic critical regime is relatively narrow and beta = 0.36+/-0.02. This result is consistent with expectations from symmetry arguments based on a Landau-type model which suggests standard three-dimensional XYcriticality.