X-ray study of the charge-density-wave transition in single-layer TiS e 2

Synchrotron x-ray studies of single-layer $\mathrm{TiS}{\mathrm{e}}_{2}$ reveal displacements of the Ti and Se atoms as a function of temperature. The measurements, with a high sensitivity of 0.001 \AA{}, show a (2 \ifmmode\times\else\texttimes\fi{} 2) charge-density-wave (CDW) structure at temperatures below a critical temperature of ${T}_{\mathrm{C}1}=233\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The temperature dependence follows a BCS-like second-order mean-field behavior. A five-layer $\mathrm{TiS}{\mathrm{e}}_{2}$ film also exhibits a CDW transition of the same character but at a lower transition temperature of ${T}_{\mathrm{C}5}=204\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is the same as that for bulk $\mathrm{TiS}{\mathrm{e}}_{2}$. The results demonstrate that lattice distortion is an integral part of the CDW transition that must also involve renormalization of the electronic structure.