Spatial properties of the photoinduced transition in Pr0.7Ca0.3MnO3

Temporal and spatial properties were investigated for the recently discovered photoinduced insulator to metal transition in Pr0.7Ca0.3MnO3. Time evolution of the photocurrent upon irradiation with a laser pulse and its laser-power and applied-voltage dependence were measured and analyzed. Irradiation patterns were controlled and sample length and width were varied. Two components of the photocurrent were separated. The slow component which was concluded to be critical for the transition, was suggested to originate from small metallic ''islands'' being created within the electrode gap by the irradiation. Measurements done on samples with the controlled width gave proof of the shrinking of the conduction path with decreasing current, supporting the picture of the conduction path being under stress from the surrounding charge ordered, antiferromagnetic bulk and being sustained by the current. Lack of dependence of the resistance on the sample length was observed, indicating that the major contribution to the voltage drop is determined by some ''neck'' in the conduction path.