Pinczuk et al. proposed the "Raman scattering by polaritons in tetragonal BaTiO3". According to the researchers, their data "also exhibit the interference effect on the 170 cm -1 mode previously identified by Rousseau and Porto. This was assigned to an interference between first and second order bands. In view of [their] results concerning the mode at 270 cm -1 , the possibility has to be considered that the interference occurs between (bands corresponding to) two q ≈ 0 TO phonons. Such an interference can occur when the two TO phonons are anharmonically coupled to the same (two or more) acoustical phonons" .