CRITICAL PHENOMENA OF THE SPIN-PEIERLS TRANSITION IN CUGEO3

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