The Phonon Modes with Strong Electron–Phonon Interactions in p- and n-Type High Tc Superconductors

The phonon modes with strong electron–phonon interactions were investigated by two-phonon Raman scattering in p- and n-type high T c superconductors. In p-type superconductors, the strong electron–phonon interaction mode changes from the breathing mode at (π, π) to the half breathing mode at (π, 0) as carrier density increases across the optimum doping in LSCO or the 60 K phase in YBCO. It is in good accordance with the change of the superconducting coherent peak position in k-space. In n-type superconductors, the strong electron–phonon interaction modes change from (0.4π, 0.4π) to (0.4π, 0) at the insulator–superconductor transition. Electron–phonon interactions play an important role in superconductivity.