ANOMALOUS SHIFTS OF OXYGEN MODE FREQUENCIES IN LA2-XSRXCUO4, YBA2CU3O7-DELTA, AND TL2BA2CA1-XGDXCU2O8 STUDIED BY PHOTOINDUCED INFRARED-ABSORPTION AND RAMAN-SPECTROSCOPY

Comparison of photoinduced local modes (PILM's) of insulating YBa2Cu3O6.3 and Tl2Ba2Ca(1-x)Gd(x)Cu2O8 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 La2CuO4, 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.