Superconductivity produced by electron doping inCuO2-layered compounds
We have discovered that the ${\mathrm{Ce}}^{4+}$ doping and subsequent annealing in reducing atmosphere give rise to 24-K superconductivity in the ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$-type structure with sheets of Cu-O squares. In contrast to the previously reported high-${\mathrm{T}}_{\mathrm{c}}$ cuprates, the charge carriers in the new superconductors are doped electrons, not holes; this was confirmed by the measurements of Hall and Seebeck coefficients as well as by chemical analysis of the effective copper valence. An anomalous dependence of ${\mathrm{T}}_{\mathrm{c}}$ on the concentration of doped electrons is shown for these electron-doped superconducting suprates.