Unusual dispersion and line shape of the superconducting state spectra of Bi2Sr2CaCu2O8+delta

Photoemission spectra of Bi2Sr2CaCu2O8+delta below T-c show two features near the (pi, 0) point of the zone: a sharp peak at low energy and a higher binding energy hump. We find that the sharp peak persists at low energy even as one moves towards (0,0), while the broad hump shows significant dispersion which correlates well with the normal state dispersion. We argue that these features are naturally explained by the interaction of electrons with a sharp mode which appears only below T-c and speculate that the latter may be related to the resonance seen in recent neutron data.