Raman and Infrared Studies of Oxide Superconductors (La1-xMx)2CuO4

Raman and infrared studies of lattice vibrations in new superconductors (La1-xMx)2CuO4 are presented. The 664 cm-1 mode which shows resonant enhancement in La2CuO4 is assigned to the planar breathing mode which strongly interacts with electrons at EF. This resonant scattering is produced by the electronic transition spanning the quasi-square Fermi surface to the nesting directions. In the spectra of Im(ε) a strong peak appears at 246 cm-1 on substituting Sr for La. It is suggested that this mode is related to the electronic transition.