Commensurate fluctuations in the pseudogap and incommensurate spin-Peierls phases of TiOCl

X-ray scattering measurements on single crystals of TiOCl reveal the presence of commensurate dimerization peaks within both the incommensurate spin-Peierls phase and the so-called pseudogap phase above TC2. This scattering is relatively narrow in Q-space indicating long correlation lengths exceeding ∼100Å below T*∼130K. It is also slightly shifted in Q relative to that of the commensurate long range ordered state at the lowest temperatures, and it coexists with the incommensurate Bragg peaks below TC2. The integrated scattering over both commensurate and incommensurate positions evolves continuously with decreasing temperature for all temperatures below T*∼130K.