Anomalous shifts of oxygen-mode frequencies in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$, ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_8$ studied by photoinduced infrared absorption and Raman spectroscopy

Comparison of photoinduced local modes (PILM’s) of insulating ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.3}$ and ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$ with Raman spectra of their metallic counterparts suggests that carrier injection anomalously increases the frequencies of phonons involving z-axis apex-oxygen motion in both the dilute (insulator) and concentrated (metallic) limit. In ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$, we observe PILM’s whose frequencies suggest a correspondence with the ‘‘ghost modes’’ observed in neutron scattering [Rietschel et al., Physica C 162–164, 1705 (1989)]. These data, together with Raman data on apex-oxygen anharmonicity, enable us to discuss the vibronic mode couplings involved in polaron formation in the three materials.