PHOTOGENERATED CARRIERS IN LA2CUO4, YBA2CU3O7-DELTA AND TL2BA2CA(1-X)GDXCU2O8 - POLARIZABILITY-INDUCED PAIRING OF POLARONS

Photo-induced absorption measurements have been carried out in the infrared spectral range on Tl2Ba2Ca(1-x)GdxCu2O8 (× = 0.02), YBa2Cu3O7-δ (δ = 0.75) and La2CuO4. In all three materials, the observation of infrared active vibrational (IRAV) modes and an associated electronic transition with common intensity and temperature dependence indicate the formation of self-localized polarons as photogenerated carriers. The photo-induced electronic transition deep in the infrared implies a major shift of oscillator strength leading to a large local polarizability in the vicinity of the polaron. The dynamic mass (Md) associated with the distortion around the charge carriers and the associated gap state energy are correlated with Tc of the superconducting phase of each materials.