ARPES on Strongly Overdoped Bi2212

The pairing interaction of the high–T_c cuprate superconductors is widely understood to have a strong d–wave spin fluctuation component which has not yet been spectroscopically studied in isolation due to the presence of competing orders that are present at most doping levels. Nevertheless, beyond a critical hole doping level p_c > 0.19, the pseudogap disappears in a first–order transition, while further doping reduces the strength of the pairing contribution from electron–phonon coupling. Its gap–to–T_c ratio of 4.3 hints that the resulting superconductor is likely described by BCS theory. It possesses sharp quasiparticle peaks in both normal and superconducting states.

ARPES measurements were carried out on hole–doped Bi2212. As–grown Bi2212 samples were cleaved in ultra high vacuum and annealed in situ under high temperature and ozone pressure, further doping it towards the end of the superconducting dome and into the vicinity of a Lifshitz transition of the antibonding band, producing a flat band around the antinode that enhances superconducting phase fluctuations which are possibly responsible for extinguishing superconductivity at the end of the dome. Subsequent rounds of vacuum annealing reduced the extent of hole doping. Doping levels were deduced from Luttinger volume, and T_c from singular in–gap spectral intensity. Details of superconducting gaps near the end of the dome and their ramifications on the nature of the pairing are discussed.