Spectral Function of Superconducting Cuprates near Optimal Doping

We argue that the unusual peak-dip-hump features observed in photoemission experiments on Bi2212 at $T\ll T_c$ can be explained by the interaction of the fermionic quasiparticles with overdamped spin fluctuations. We show that the strong spin-fermion interaction combined with the feedback effect on the spin damping due to superconductivity yields the fermionic spectral function $A({\mathbf{k}}_F,\omega )$ which simultaneously displays a quasiparticle peak at $\omega =\Delta$ and a broad maximum (hump) at $\omega \gg \Delta$. In between the two regimes, the spectral function has a dip at $\omega \sim 2\Delta$. We argue that our theory also explains the tunneling data.