Superconductivity-induced changes of the phonon resonances in RBa₂Cu₃O₇ (R=rare earth)

We observe a characteristic energy $\hbar\omega_{c}\approx 2.1$ eV which separates regions of different behavior of the phonon intensities in the Raman spectra of the $R\rm Ba_2Cu_3O_7$ system. A superconductivity-induced drop of phonon intensities is found for the oxygen modes O(4) and O(2)-O(3) only for excitation energies below $\hbar\omega_c$. This intensity drop indicates an order parameter which affects energies in the vicinity of $\hbar\omega_c$.