Action spectra of the two-stage photoinduced insulator-metal transition inPr1−xCaxMnO3

The action spectra for the photoinduced insulator-metal transition in ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ were investigated in the $0.45-3.05\hspace{0.5em}\mathrm{eV}$ range. The photon-density threshold for the transition exhibits a gaplike behavior at $\sim 0.4\hspace{0.5em}\mathrm{eV}$ 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.