Raman line shapes of anharmonic phonons

Anharmonic effects in crystals typically result in the symmetric broadening of the single-phonon Lorentzian line shape. However, a simple model, based on consideration of a highly anharmonic potential, shows that anharmonicity can lead not only to asymmetric line shapes but also to line shapes composed of multiple subpeaks. Experimental Raman data on the soft A1(TO) phonon in ferroelectric PbTiO3 indicates that this mode does indeed consist of a series of subpeaks whose intensities are accurately predicted (with no fitting parameters) by our model