SPECTRAL WEIGHT CHANGES AT THE SUPERCONDUCTING TRANSITION OF BI2SR2CACU2O8+DELTA

We overview our recent angle-resolved photoemission studies of the spectral weight changes that occur at the superconducting transition of Bi2Sr2CaCu2O8+delta. We have found that (1) as the sample goes superconducting, not only is there spectral weight transfer from the gap region to the pile-up as in BCS theory, but along the GAMMA-MBAR direction there is also some spectral weight transfer from higher binding energies in the form of a dip, (2) at the superconducting transition there is a decrease (increase) in the occupied spectral weight for the spectra taken along GAMMA-MBAR (GAMMA-X), (3) the magnitude of the superconducting energy gap appears to be anisotropic in the k(xy) plane, and (4) for the overdoped Bi2Sr2CaCu2O8+delta samples that we studied the gap DELTA appears to fall off much more rapidly with doping than does the T(C). Recent theoretical attempts to understand our data are briefly reviewed.