Pressure dependence of the superconducting transition temperature of superoxygenatedLa2CuO4+δ

Abstract

We report the pressure dependence of the superconducting transition temperatures (${\mathit{T}}_{\mathit{c}}$) of two phases of superoxygenated ${\mathrm{La}}_2$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$ prepared by both high-pressure and electrochemical charging with oxygen. The results are strikingly different from those observed in ${\mathrm{La}}_{1.85}$ ${\mathrm{Sr}}_{0.15}$ ${\mathrm{CuO}}_4$, which has a similar maximum value for ${\mathit{T}}_{\mathit{c}}$. The results are discussed in the framework of a model in which a positive contribution to the pressure derivative ubiquitous to the copper oxide superconductors is canceled to varying degree by a negative derivative due to charge transfer associated with oxygen mobility which depends upon the temperature at which the pressure is applied.