A Brillouin scattering study of La_0.77Ca_0.23MnO₃ across the metal–insulator transition

Temperature-dependent Brillouin scattering studies have been carried out on La0.77Ca0.23MnO3 across the paramagnetic insulator–ferromagnetic metal (I–M) transition ( 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 TC. The temperature dependence of the SRW and HVPSAW modes is related to the increase in the elastic constant C11 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 TC.