Oxygen isotope effect in a high-temperature superconductor under high pressure

The role of phonons is addressed by combining the information obtained from the measurements of Raman scattering and magnetic susceptibility in an optimally doped high-temperature superconductor. We show that the high-pressure behavior of the oxygen isotope exponent can be predicted from the changes in both the phonon frequency and superconducting transition temperature based on a phonon-mediated d-wave BCS-like model. The isotope exponent is found to decrease with increasing pressure but remain small and positive within the pressure regime studied. These results point to the important role of the electron-phonon interaction for high-temperature superconductivity.