Evidence of Polaronic Deformations in High Tc Materials Observed by Photo-Induced IR Absorption and Photo-Induced XAS

Doping the semiconducting parent compound of the high temperature superconducting systems by laser illumination is used to investigate possible charge- phonon interaction in the normal state. In this paper we present an analysis of the lattice distortions induced by photogenerated carriers in different families of cuprate perovskites like YBa2Cu3O6+x, La2CuO4, and Nd2CuO4. Comparison of photoinduced (PA) features with doping induced modes and with Raman scattering measurements of semiconducting and metallic systems reveals strong similarities between most of the observed PA vibrational mode and those (Raman or IR) of the superconducting material. In order to investigate the microscopic photoinduced structural and electronic variation in ErBa2Cu3O6+x we have also performed photoinduced X-ray absorption spectroscopy (P-XAS). The results indicate that a contraction of the in plane copper (Cu(2)) and apical oxygen (0(4)) bond occurs and also that the photoinjected holes responsible of the distortion are situated on 0(4) with pz symmetry. A comparison of our findings with possible theoretical scenarios is also presented.