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 T_C2. This scattering is relatively narrow in Q-space indicating long correlation lengths exceeding ∼100 Å below T^*∼130 K. 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 T_C2. The integrated scattering over both commensurate and incommensurate positions evolves continuously with decreasing temperature for all temperatures below T^*∼130 K.