Critical phenomena at the spin-Peierls transition in MEM(TCNQ)2

We have performed a detailed x-ray scattering study of the critical phenomena associated with the spin-Peierls phase transition in the organic compound MEM(TCNQ)2. Analysis of the superlattice reflection intensity indicates an order parameter with an associated critical exponent β=0.35±0.06 consistent with three-dimensional behavior, as seen in the inorganic compound CuGeO3, and clearly inconsistent with mean field behavior, as indicated in …