Temperature dependence of the Raman scattering from CuCl

Abstract

Temperature dependence of the Raman scattering from CuCl has been measured from room temperature down to 7 \ifmmode^\circ\else\textdegree\fi{}K. The LO-mode frequency shows a slight decrease at low temperatures, apparently mirroring the low-temperature negative thermal expansion. An unambiguous observation of the TO-mode scattering is not made because of the curious $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ double peak anomaly described by Kaminow and Turner. Discrepancies in the Lyddane-Sachs-Teller relation may be accounted for by using for ${\ensuremath{\omega}}_{\mathrm{TO}}$ a weighted average of the $\ensuremath{\beta}$- and $\ensuremath{\gamma}$-mode frequencies; measurements of ${\ensuremath{\epsilon}}_{0}$ have been extended down to 7 \ifmmode^\circ\else\textdegree\fi{}K to verify this assumption. Attempts to fit the observed spectrum in the region of the $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ peaks using available uncoupled- and coupled-mode theories are described.