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

Abstract

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 $\mathbf{Q}$-space indicating long correlation lengths exceeding $\ensuremath{\sim}100\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ below ${T}^{*}\ensuremath{\sim}130\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It is also slightly shifted in $\mathbf{Q}$ 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 ${T}^{*}\ensuremath{\sim}130\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.