Action spectra of the two-stage photoinduced insulator-metal transition in Pr_1-xCa_xMnO₃

The action spectra for the photoinduced insulator-metal transition in Pr_1-xCa_xMnO₃ were investigated in the 0.45-3.05eV range. The photon-density threshold for the transition exhibits a gaplike behavior a∼0.4eV with anisotropic features, and it is insensitive to the degree of carrier doping x. A two-stage mechanism is proposed for the transition. In the first stage, photoexcited charge carriers melt down the charge-ordered state by screening effects, which is followed by a local formation of metastable metallic domains. In the second stage, the barrier between the metallic domains is overcome by an applied electric field resulting in a continuous conducting path that remains stable as long as the current is maintained.