Ultrafast dynamics in Pr-doped and oxygen-deficient YBCO films by femtosecond spectroscopy

We have systematically measured the transient reflectivity (Delta R/R) in P r-doped YBCO (PrxY1-xBa2Cu3O7) and partially oxygen deficient YBCO (YBa2Cu3 O7-delta) thin films at temperatures ranging from 300 to 12 K by using the femtosecond pump-probe technique. Measurements performed at low temperature s indicate that the magnitude, polarity, and relaxation time of the transie nt reflectivity is strongly dependent on the photon energy and pumping inte nsity of the optical excitation, the ambient temperature, and the doping le vel of the superconducting thin films. Moreover, the temperature dependence of the Fermi-level position was also observed. (C) 2000 Elsevier Science B .V. All rights reserved.