Percolative superconductivity in electron-doped Sr1-xEuxCuO2+y films

Electron-doped infinite-layer Sr1-xEuxCuO2+y films over a wide doping range have been prepared epitaxially on SrTiO3(001) using reactive molecular beam epitaxy. In-plane transport measurements of the single-crystalline samples reveal a dome-shaped nodeless superconducting phase centered at x -0.15, a Fermi-liquid behavior and pronounced upturn in low-temperature resistivity. We show that the resistivity upturn follows square-root temperature dependence, suggesting the emergence of superconductivity via a three-dimensional percolation process. The percolative superconductivity is corroborated spectroscopically by imaging the electronic phase separation between superconducting and metallic phases with low-temperature scanning tunneling microscopy. Furthermore, we visualize interstitial and apical oxygen anions that rapidly increase in number as x > 0.12 and elucidate their impacts on the superconductivity and normal-state resistivity.