Raman-scattering study of crystal-field excitations inPr2CuO4

Crystal-field transitions within the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{H}}_4$ multiplet of ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$ were studied by Raman scattering as a function of temperature. We observed three crystal-field excitations at 156, 540, and 675 ${\mathrm{cm}}^{\mathrm{-}1}$. The peak at 156 ${\mathrm{cm}}^{\mathrm{-}1}$, assigned by other authors to the lowest ${\mathit{E}}_{\mathit{g}}$ phonon mode, shows a thermal broadening of the linewidth, which is the signature for acoustical-phonon-relaxation processes between crystal-field levels. Our results are in excellent agreement with recent inelastic neutron scattering experiments in ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$.