SYMMETRY DEPENDENCE OF PHONON LINE-SHAPES IN SUPERCONDUCTORS WITH ANISOTROPIC GAPS

The temperature dependence below T(c) of the line shape of optical pho nons of different symmetry as seen in Raman scattering is investigated for superconductors with anisotropic energy gaps. It is shown that th e symmetry of the electron-phonon vertex produces nontrivial couplings to an anisotropic energy gap which leads to unique changes in the pho non line shape for phonons of different symmetry. The phonon line shap e is calculated in detail for B1g and A1g phonons in a superconductor with d(x2-y2) pairing symmetry. The role of satellites peaks generated by the electron-phonon coupling are also addressed. The theory accoun ts for the substantial phonon narrowing of the B1g phonon, while narro wing of the A1g phonon which is indistinguishable from the normal stat e is shown, in agreement with recent measurements on Bi2Sr2CaCu2O8 and YBa2Cu3O7.