63Cu-NMR/NQR studies on apical-F bi-layered cuprates Ba2CaCu2O4F2 and Ba2CaCu2O4(F1.6O0.4)

We report 63Cu-NMR/NQR on the bi-layered high-Tc copper oxide Ba2CaCu2O4F2, which is expected to be a Mott insulator in an ideal case of a nominal content of fluorine, and less fluorinated Ba2CaCu2O4(F1.6O0.4) to clear the doping mechanism in apical-fluorine multilayered system Ba2Can-1CunO2nF2, where n is the number of the layers in a unit cell. In the case of n=3 and, especially, n=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 CuO2 plane (IP) and the outer one (OP), keeping Cu+2 on average. It is revealed that Ba2CaCu2O4F2 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=3 and 4, and that we should reconsider the self-doping mechanism as the carrier source in the apical-fluorine system.