Fig. 4: Measured chemical potential shift with electron doping in Ca₃Cu₂O₄Cl₂.

a–c Doping evolution of O 2p orbitals at Γ (a) and (π, π) (b), and Ca 3p core level (c). Symbols in (a–c) indicate the respective spectral peaks. The photoemission spectra of the undoped parent compound in a larger energy scale are shown in the respective insets. d Chemical potential shift with electron doping determined from the three types of measurements in (a), (b), and (c). The chemical potential shift for the undoped parent compound is set at zero as a reference. The chemical potential shifts obtained from the three cases give a similar result with a jump of ~1 eV in the initial Rb-deposition stage. Error bars reflect the uncertainty in determining the EDC peak positions.