SUPERCONDUCTIVITY-INDUCED PHONON SELF-ENERGY EFFECTS IN HIGH-TC SUPERCONDUCTORS

The superconductivity-induced self-energy of phonons has been calculated in the lowest-order conserving approximation using conventional strong-coupling theory and also including scattering at nonmagnetic impurities. Results for the dependence of the shift and the width of phonons on temperature and scattering rates are presented and their sensitivity on the strength of the electron-phonon coupling and on impurities is pointed out. The theory is applied to optical data in YBa2Cu3O7 using the experimental one-phonon density, the value of Tc and [*=0.25 as inputs. Neglecting anisotropies and the momentum dependence of the electron-phonon coupling the resulting strong-coupling model with λ≈2.9 yields results which are in good agreement with the data, in particular, if impurity scattering is taken into account. © 1990 Springer-Verlag.