Nonlinear electrical response in a non-charge-ordered manganite:Pr0.8Ca0.2MnO3

Up to now, electric-field-induced nonlinear conduction in the ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ system (PCMO) has been ascribed to a current-induced destabilization of the charge ordered phase. However, for $x<~0.25,$ a ferromagnetic insulator state is observed, and charge ordering (CO) is absent whatever the temperature. A systematic investigation of nonlinear transport in the ferromagnetic insulator ${\mathrm{Pr}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_3$ shows rather similar results to those obtained in charge-ordered systems. However, the experimental features observed in ${\mathrm{Pr}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_3$ are distinct in that the collapse of the CO energy gap cannot be invoked as is usually done in the other members of the PCMO system. We propose interpretations in which the effectiveness of the double exchange is restored upon application of an electric field.