Change of Fermi-surface topology in Bi2Sr2CaCu2O8+δ with doping

We report the observation of a change in Fermi-surface topology of Bi₂Sr₂CaCu₂O_8+δ with doping. By collecting high-statistics angle-resolved photoemission spectroscopy data from moderately and highly overdoped samples and dividing the data by the Fermi function, we answer a long-standing question about the Fermi-surface shape of Bi₂Sr₂CaCu₂O_8+δ close to the (π,0) point. For moderately overdoped samples (T_c=80K) we find that both the bonding and antibonding sheets of the Fermi surface are hole like, but for a doping level corresponding to T_c=55K we find that the antibonding sheet becomes electron like. Similar observations of a topology change were observed in La_2-xSr_xCuO₄ and in Bi₂Sr₂CuO_6+δ . On the other hand, whereas this critical doping value in single-layer materials corresponds to a T_c near zero, it occurs at a smaller doping value in the double-layer case where T_c is still quite high (the difference in doping levels is due to the bilayer splitting). This argues against a van Hove singularity scenario for cuprate superconductivity.