Jahn-Teller Dynamics in Charge-Ordered Manganites from Raman Spectroscopy

The Raman spectra of the charge-ordered manganite ${\mathrm{Pr}}_{0.65}{\mathrm{Ca}}_{0.35}{\mathrm{MnO}}_3$ were studied as functions of temperature and excitation energy and compared to magnetic moment and electrical conductivity behaviors. Both the charge ordering ( $T_{\mathrm{co}}\approx 225\mathrm{K}$) and the antiferromagnetic transitions ( $T_N\approx 175\mathrm{K}$) affect the spectral shape and intensity, indicating strong charge-lattice and spin-lattice couplings. Below $T_{\mathrm{co}}$ a transition from dynamic Jahn-Teller distortions to a collective static distortion takes place. A change of the spectra is observed on increasing the excitation energy above 2.5 eV and it is attributed to a resonant polaron excitation.