Polarization effects in photoemission disentangle the origin of the shadow bands in Bi-based superconductors

Angle-resolved photoemission spectroscopy has been used to investigate the origin of the shadow bands present at the Fermi surface of bismuth-based superconductors. Momentum distribution curves along the ΓY high-symmetry direction and Fermi surface maps measured on Bi₂ Sr₂ CaCu₂ O_8+δ (Bi2212) single crystals with two different doping levels have revealed that the shadow bands and the main bands have different initial state symmetry. This result implies that the orthorhombicity exhibited by these materials cannot be responsible for their emergence at the Fermi surface.