Electric current induced extrinsic asymmetric – behavior in epitaxial thin films on single crystal substrates

The electric current effects on (La,Ca)MnO3 thin films epitaxially grown on SrTiO3 and LaAlO3 substrates were carefully investigated. When the applied electric current density exceeds a sample dependent critical value, apparent asymmetric I – V curves are clearly observed on the stimulated (La,Ca)MnO3/SrTiO3 films. The larger current and longer processed time enhance the asymmetry. No asymmetry was observed on all the (La,Ca)MnO3/LaAlO3 films independent of applied electric current and stimulated time. The comparison study indicates that the observed asymmetric I – V behavior of the (La,Ca)MnO3/SrTiO3 films is closely related to the electric field induced conductivity of the underlying SrTiO3 substrates. We proposed an equivalent circuit to qualitatively explain our results. Our results also imply that in dealing with the electric current (field) effects on the thin films fabricated on SrTiO3 substrates, the electric field induced conductivity of the substrates should be considered.