High-temperature superconductivity in tetragonal perovskite structures: Is oxygen-vacancy order important?

Abstract

We used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to substitute preferentially on the Cu(2) and Cu(1) sites in the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ superconductor. Small doping of Ga induces an orthorhombic-to-tetragonal structural transition, but the values of ${\mathrm{T}}_{\mathrm{c}}$ are as high as 81 K in the tetragonal phase. Our results indicate that the oxygen-vacancy order, or the linear-chain structure, is not essential. We also find that the Cu(2) sites are much more crucial than the Cu(1) sites in sustaining the high ${\mathrm{T}}_{\mathrm{c}}$.