Photoinduced insulator-metal transition in La0.81MnO3/Al2O3/Nb tunnel junctions

We report the effect of illumination by ultraviolet and visible light on th e resistance versus temperature and current versus voltage characteristics of La0.81MnO3/Al2O3/Nb tunnel junctions. Under illumination, the resistance of tunnel junctions follows the resistance in darkness at high temperature s but at temperatures lower than 95 K, the illumination induces a colossal decrease of the resistance. This is a transient effect because the changes are reversible when the light is switched on and off. Changes of the electr ical properties under illumination were seen for the tunnel junctions only and not in the epitaxial La0.81MnO3 electrode which shows a classical insul ator-metal transition at temperature T-c = 285 K. We explain this effect by a photoinduced insulator-metal transition of the oxygen depleted manganite interface close to the tunnel barrier which changes dramatically the width of the barrier. (C) 2001 American Institute of Physics.