Symmetry of the Gap Deduced from the Phonon Renormalization

The influence of the gap anisotropy on the superconductivity induced renormalization of q = 0 phonons is studied. An analytical expression for the shift and the broadening of the phonon lines is derived in second order of the electron-lattice coupling. The full k-dependency of the gap function is taken into account. The renormalization is calculated numerically for different anisotropies of the gap (s-wave, d-wave...) And compared to Raman experiments. The value of the hole-lattice coupling in the high-Tc materials can be estimated