Femtosecond spectroscopic studies of photodoping effects in insulating YBa2Cu3O6+x and Nd2CuO4 thin films

Abstract We have investigated photodoping effects in insulating YBa 2 Cu 3 O 6.2 and Nd 2 CuO 4 , which are parent materials of high T C superconductors, by means of femtosecond pump-probe spectroscopy using white continuum light. The absorption changes are observed in the wide energy region after the irradiation of the femtosecond laser pulse. The spectral features of the absorption change are in good agreement with the change by the doping with changing the chemical composition, and this indicates that the electronic structures in the CuO 2 planes are drastically changed by femtosecond laser pulses. The photo-induced change in the electronic structure suggests the formation of the optically induced in-gap state with the decay time of ∼ 1 ps. Furthermore, we have investigated the photodoping effect by changing the photon energies of the pumping pulse.