Photoinduced absorption from localized intra-gap states

A model is developed for photoinduced absorption from localized states obse rved in femtosecond pump-probe experiments in high-T-c, superconductors and other materials. The dynamics of localized carriers are described in terms of phenomenological approach similar to that originaly proposed by Rothwar f and Taylor. Expanding the relaxation rate in powers of the order paramete r we have shown that density of localized carriers is sensitive to T-c. Fro m the analysis of the experimental data on YBa2Cu3O7-x and K0.3MoO3. We con clude that significant intra-gap density of localized states exists in thes e materials. Temperature dependence of the density of photoexcited localize d carriers in underdoped YBa2Cu3O7-x and in K0.3MoO3 is consistent with the observation of the pseudogap above T-c.