Percolative Superconductivity in Electron-Doped Sr${}_{1-x}$Eu${}_x$CuO${}_{2+y}$ Films

Abstract

Electron-doped infinite-layer Sr${}_{1-x}$Eu${}_x$CuO${}_{2+y}$ films over a wide doping range have been prepared epitaxially on SrTiO${}_3$(001) using reactive molecular beam epitaxy. In-plane transport measurements of the single crystalline samples reveal a dome-shaped nodeless superconducting phase centered at $x$ $\sim$ 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.

5 pages, 4 figures, 9 supplemental figures