Raman active phonons in Tl-based high-T_c superconductors

We explore the symmetries and structural similarities within the single layer Tl high-Tc materials with n immediately adjacent Cu-O planes, which we designate 1-Tl(n). The same approach is taken for the double layer Tl materials, called 2-Tl(n). YBa2Cu3O7-δ is a special case of 1-Tl(2). With this understanding, an excellent overview of Raman active modes can be ma de and some new Raman data are presented. We find that the frequencies that should be similar within and between these two families are understood, as well as the phonon modes that should be different. The agreement with experiment is good and this understanding simplifies mode assignments and should help to pinpoint Raman modes which are not intrinsic. © 1990.