Oxygen-isotope effect on the high-frequency Raman phonons in Bi2Sr2CaCu2O8+δ

Abstract

Raman spectra have been obtained from single-crystal samples of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\mathrm{\delta }\mathrm{}}$ with varying degrees of oxygen-isotope exchange. A comparison of the high-energy $(>~400{\mathrm{cm}}^{-1})$ vibrational spectra obtained from an unexchanged sample, a partially exchanged sample and a fully exchanged crystal has been carried out to obtain an unambiguous assignment of the $A_{1g}$ modes at 465 and $630\hspace{0.5em}{\mathrm{cm}}^{-1}.$ The 465 mode is assigned to c-axis vibrations of O(3) atoms in the Bi-O layers and the 630 mode to the O(2) apical oxygen atoms in the Sr-O layers.