Electron–boson coupling and oxygen-isotope effect in the optical conductivity of high-Tc superconductors

Abstract We have investigated electron–boson coupling in the optical conductivity of high- T c superconductors through the optical self-energy. The real part of the self-energy (Re Σ op ( ω )) of YBa 2 Cu 3 O y (YBCO) shows a characteristic doping dependence. In the optimally doped YBCO, Re Σ op ( ω ) has a single peak around 65 meV, which corresponds to the kink structure of the band dispersion. On the other hand, in the under-doped YBCO, the peak structure of Re Σ op ( ω ) splits into two parts. To evaluate contribution from the phonons in electron–boson coupling, we have measured oxygen-isotope effects by substituting 16 O→ 18 O for the optimally doped and under-doped YBCO.