Evolution of the electronic structure with doping in Bi2Sr2CaCu2O8+delta - Angle resolved photoemission results

We present experimental results showing that the electronic strucure of the high Tc cuprate superconductors evolves from having large pieces of Fermi surface (FS) at high doping levels to small pieces of FS centered at (pi/2,pi/2) at low doping levels. The dramatic change in the FS occurs with only subtle changes in the electronic structure, which occur mostly near the (pi,0) point of the Brillouin zone. We suggest that this evolution is intimately related to the evolution of the antiferromagnetic (AF) order with doping.