Impact of Optical Modes on the Pairing Potential in Bilayer Cuprates
  Superconducting transition temperature is calculated for differently doped bilayer cuprates. Superexchange is assumed to be the dominating mechanism of high-temperature superconductivity, but the contribution from the phonon potential is not negligible, which qualitatively explains the observed weak isotopic effect. The calculated value 2$\Delta_{max}/k_B T_C \simeq 4.5$ is close to the experiment in the case of optimum doping. 
I.A. Larionov and M.V. Eremin