Electronic mechanism of critical temperature variation inRBa2Cu3O7−δ

Abstract

We have performed systematic studies of the trend of the critical temperature ${T}_{c}$ due to both Madelung site potential difference between in-plane oxygen and copper sites $\ensuremath{\Delta}{V}_{\mathrm{M}}$ and interlayer effect in the optimally doped 123 superconductors $R{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. $\ensuremath{\Delta}{V}_{\mathrm{M}}$ is found to decrease with the increase of the trivalent rare-earth ionic radius ${r}_{{R}^{3+}}$. This change enhances the next-nearest-neighbor hopping integral ${t}^{\ensuremath{'}}$, which results in the experimentally observed increase of ${T}_{c}$ with ${r}_{{R}^{3+}}$. The coherent interlayer single-particle hopping ${t}_{\ensuremath{\perp}}$ has a more profound effect than ${t}^{\ensuremath{'}}$ on the nearly linear trend of ${T}_{c}$ as a function of ${r}_{{R}^{3+}}$. These results reveal the importance of the electronic origin of the rare-earth ionic size effect on ${T}_{c}$ in this family.