Superconductivity phase diagrams for the electron-doped cuprates R2−xCexCuO4 (R=La, Pr, Nd, Sm, and Eu)

Abstract

The superconductivity phase diagrams of electron-doped cuprates of the form $R_{2-x}{\mathrm{Ce}}_x\mathrm{Cu}{\mathrm{O}}_4$ (with $R=\mathrm{La}$, Pr, Nd, Sm, and Eu) have been determined for cerium compositions $0<x<0.36$ in a consistent series of epitaxial thin films grown by reactive molecular beam epitaxy. The use of epitaxial thin films allows the growth of materials away from thermodynamical equilibrium expanding the accessible phase space beyond the availability of bulk material. The superconducting phase space systematically increases with the rare-earth ionic size. The doping concentration where the maximal transition temperature occurs in ${\mathrm{La}}_{2-x}{\mathrm{Ce}}_x\mathrm{Cu}{\mathrm{O}}_4$ is considerably shifted to lower doping $(x\sim 0.09)$ compared to ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ $(x\sim 0.15)$. At the same time, the width of the superconducting region is broadened.