Polarizability and single-particle spectra of two-dimensional s- and d-wave superconductors

We present analytic results for the polarizabilities chi(Q,omega), in the c harge, spin, and current channels for two-dimensional s- and d-wave superco nductors for large momentum transfer. A collective mode in the charge chann el is predicted to exist for extremum vectors of the Fermi surface with ene rgy below twice the maximum superconducting gap. Such modes are directly ob servable through inelastic x-ray or electron scattering. Scattering of sing le particle excitations by these collective modes leads to several unusual features in the single particle spectrum in the superconducting state which are seen in angle resolved photoemission experiments. [S0163-1829(98)03845 -4].