Superconductivity produced by electron doping in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>-layered compounds

Abstract

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.