Superconductivity induced by structural reorganization in the electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_4$

Electron-doped and hole-doped superconducting cuprates exhibit a symmetric phase diagram as a function of doping. This symmetry is however only approximate. Indeed, electron-doped cuprates become superconductors only after a specific annealing process: This annealing affects the oxygen content by only a tiny amount, but has a dramatic impact on the electronic properties of the sample. Here we report the occurrence of superconductivity in oxygen-deficient Nd$_{2-x}$Ce$_x$CuO$_4$ thin films grown in an oxygen-free environment, after annealing in pure argon flow. As verified by x-ray diffraction, annealing induces an increase of the interlayer distance between CuO$_2$ planes in the crystal str…