Plane oxygen vibrations and their temperature dependence inHgBa2Ca2Cu3O8+δsingle crystals

Abstract

A polarized Raman-scattering investigation of ${\mathrm{HgBa}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ single crystals has been performed. The following Raman-active modes associated with oxygen vibrations in the ${\mathrm{CuO}}_{2}$ planes have been clearly identified: the ${\mathrm{B}}_{1\mathrm{g}}$ mode at 245 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, corresponding to the out-of-phase vibration of the plane oxygens, and the ${\mathrm{A}}_{1\mathrm{g}}$ mode at 265 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, corresponding to their in-phase vibration. Another defect-induced ${\mathrm{A}}_{1\mathrm{g}}$ mode was also detected at 400 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Measurements of the temperature dependence of these Raman features demonstrate that the ${\mathrm{A}}_{1\mathrm{g}}$ 265- and 400-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ modes show abrupt changes in frequency and linewidth across ${\mathrm{T}}_{\mathrm{c}}$, accompanied by an appreciable intensity enhancement in the superconducting state. However, similar ``anomalies'' were not observed for the 245-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonon of ${\mathrm{B}}_{1\mathrm{g}}$ symmetry.