Selective hybridization between the main band and the superstructure band in the Bi2Sr2CaCu2 O8+δ superconductor

High-resolution laser-based angle-resolved photoemission measurements have been carried out on Bi2Sr2CaCu2O8+δ (Bi2212) and Bi2Sr2-xLaxCuO6+δ (Bi2201) superconductors. Unexpected hybridization between the main band and the superstructure band in Bi2212 is clearly revealed. In the momentum space where one main Fermi surface intersects with one superstructure Fermi surface, four bands are observed instead of two. The hybridization exists in both the superconducting state and the normal state, and in Bi2212 samples with different doping levels. Such a hybridization is not observed in Bi2201. This phenomenon can be understood by considering the bilayer splitting in Bi2212, the selective hybridization of two bands with peculiar combinations, and the altered matrix element effects of the hybridized bands. These observations indicate that the origin of the superstructure bands is intrinsic to the CuO2 planes. Therefore, understanding physical properties and superconductivity in Bi2212 should consider the complete Fermi surface topology which involves the main bands, the superstructure bands, and their interactions.