Raman study of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$/${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superlattices

We report Raman measurements on c-axis-oriented high-${\mathit{T}}_{\mathit{c}}$ ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$/${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superlattices. The assignment of the observed phonon lines is obtained from a comparison of the Raman spectra of these superlattices, bulk ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, and also of an (Y/Pr)${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ mixed crystal. Vibrational peaks were found corresponding to confined phonons as well as extended excitations. We find also a pronounced softening of the ${\mathit{B}}_{1\mathit{g}}$-like phonon localized in the Y layers (out-of-plane bending vibration of ${\mathrm{CuO}}_2$-plane oxygen) below the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$, a property characteristic of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superconductors, while phonons localized in ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ show no such effect.