63Cu-NMR/NQR studies on apical-F bi-layered cuprates Ba2CaCu2O4F2Ba2CaCu2O4F2 and Ba2CaCu2O4(F1.6O0.4Ba2CaCu2O4(F1.6O0.4)

We report 63Cu-NMR/NQR on the bi-layered high-TcTc copper oxide Ba2CaCu2O4F2Ba2CaCu2O4F2, which is expected to be a Mott insulator in an ideal case of a nominal content of fluorine, and less fluorinated Ba2CaCu2O4(F1.6O0.4Ba2CaCu2O4(F1.6O0.4) to clear the doping mechanism in apical-fluorine multilayered system Ba2Can-1CunO2nF2Ba2Can-1CunO2nF2, where n is the number of the layers in a unit cell. In the case of n=3n=3 and, especially, n=4n=4, the origin of carrier doping has been attributed to a self-doping mechanism based on the nominal stoichiometry; electrons are transferred between the inner CuO2CuO2 plane (IP) and the outer one (OP), keeping Cu+2Cu+2 on average. It is revealed that Ba2CaCu2O4F2Ba2CaCu2O4F2 is an underdoped superconductor with hole carriers  , doped by an inevitable deviation from the nominal content of apical fluorines. This result suggests that hole carriers are doped in the same manner for the case of n=3n=3 and 4, and that we should reconsider the self-doping mechanism as the carrier source in the apical-fluorine system.