Phase diagram of Bi2Sr2CaCu2O8+δ revisited

In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p . In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, T c , using the assumption that the T c dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi 2 Sr 2 CaCu 2 O 8+ δ , cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to T c = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ 0 = (4 ± 1) k B T c The doping level of cuprate superconductors is usually difficult to determine. Here, Drozdov et al. report spectroscopic studies of in-situ modified Bi 2 Sr 2 CaCu 2 O 8+ δ , exploring not only the superconducting dome but also the previously inaccessible, non-superconducting regime of the phase diagram, with absolute determination of the doping level.