Shallow core levels, or how to determine the doping and T c of Bi 2 Sr 2 CaCu 2 O 8 + δ and Bi 2 Sr 2 CuO 6 + δ without cooling
In this study, determining the doping level in high-temperature cuprate superconductors is crucial for understanding the origin of superconductivity in these materials and for unlocking their full potential. However, accurately determining the doping level remains a significant challenge due to a complex interplay of factors and limitations in various measurement techniques. In particular, in Bi 2 Sr 2 CuO 6+δ and Bi 2 Sr 2 CaCu 2 O 8+δ , where the mobile carriers are introduced by non-stoichiometric oxygen δ, the determination has been extremely problematic. Here, we study the doping dependence of the electronic structure of these materials in angle-resolved photoemission and find that both the doping level, p, and the superconducting transition temeprature, T c can be precisely determined from the binding energy of the Bi 5d core-levels. The measurements can be performed at room temperature, enabling the determination of p and T c without cooling the samples. This should be very helpful for further studies of these materials