Brillouin Scattering Studies of La_(0.77)Ca_(0.23)MnO₃ Across Metal-Insulator Transition

Temperature-dependent Brillouin scattering studies have been carried out on La_{0.77}Ca_{0.23}MnO_3 across the paramagnetic insulator - ferromagnetic metal (I-M) transition. The spectra show a surface Rayleigh wave (SRW) and a high velocity pseudo surface acoustic wave (HVPSAW) besides bulk acoustic waves (BAW). The Brillouin shifts associated with SRW and HVPSAW show blue-shifts, where as the frequencies of the BAW decrease below the I-M transition temperature (T_C) of 230 K. These results can be understood based on the temperature dependence of the elastic constants. We also observe a central peak whose width is maximum at T_C.