Uniaxial pressure dependence of the superconducting critical temperature in R${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ high-${\mathit{T}}_{\mathit{c}}$ oxides

We have obtained the three uniaxial-pressure derivatives of the critical temperature, ${\mathit{T}}_{\mathit{c}}$, for ${\mathrm{GdBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ from the hydrostatic pressure dependence measured on films of different crystalline orientations. The strain derivatives are found to be extremely anisotropic in the a-b plane, inducing a decrease (increase) of ${\mathit{T}}_{\mathit{c}}$ when compressing across (along) the CuO chains. A comparison of the results in c-oriented R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films and superlattices for various R and substrates reveals a nonmonotonic relation between the critical temperature and pressure.