Systematic Raman study of optical phonons in RBa2Cu3 O6+δ (R= Y, Dy, Gd, Sm, Nd): Antiferromagnetic coupling strength versus lattice parameters

We present a systematic study of the interplay between lattice parameters and the energy of the optical phonons as well as the antiferromagnetic coupling strength, J, in the high-Tc superconducting cuprate RBa2Cu3O6+δ (R-123, R=Y, Dy, Gd, Sm, Nd) with hole doping p (0.00<p0.04). The energy of the B1g mode at νB1g≈335cm-1 has been found to relate systematically to the inverse of the lattice parameter a. Our results confirm the temperature dependent phonon splitting for Nd-123 at low doping, which has been reported for optimally doped Nd-123. Surprisingly, J is independent of a for the first four R families, and a general consistency between Tcmax and J, as suggested in a previous investigation, could not be confirmed.