The authors report quantitative evidence from Raman scattering for the applicability of strong-coupling theory for phonon self-energies to high-Tc superconductors. Positive and negative shifts of optical phonon frequencies in the superconducting state of RBa2Cu3O74-delta fall near a universal curve when plotted vs. phonon energy. This curve is the phonon self-energy shift obtained from strong-coupling theory by Zeyher and Zwicknagl, with 2 Delta /kBTc=5.2. The appropriate electron-phonon coupling constants ( lambda =0.02 and 0.01 for the 340 and 440-cm-1 modes) were calculated ab initio.
 

Solid State Communications, 75 219-23, 1990.