A Brillouin scattering study of $ La_{ \mathrm{0.77}} Ca_{ \mathrm{0.23}}MnO_{ \mathrm{3}} $ across the metal-insulator transition

Temperature-dependent Brillouin scattering studies have been carried out on $ La_{ \mathrm{0.77}} Ca_{ \mathrm{0.23}}MnO_{ \mathrm{3}} $across the paramagnetic insulator-ferromagnetic metal (I-M) transition (T-C ~ 230 K). The spectra show modes corresponding to a surface Rayleigh wave (SRW) and a high velocity pseudo-surface wave (HVPSAW) along with bulk acoustic waves (B1 and B2). The Brillouin shifts associated with the SRW and HVPSAW increase,whereas the B1 and B2 frequencies decrease, below T-C. The temperature dependence of the SRW and HVPSAW modes is related to the increase in the elastic constant C-11 across the I-M transition. The decrease in frequency across the I-M transition of the bulk modes is understood to be due to enhanced self-energy corrections as a result of increased magnon-phonon interaction across the I-M transition. Correspondingly,these modes show a large increase in the full width at half maximum(FWHM) as the temperature decreases. We also observe a central peak whose width is maximum at T-C