Electric-field-induced melting of the randomly pinned charge-ordered states of rare-earth manganates and associated effects

Films of charge-ordered ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},$ ${\mathrm{Gd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},$ ${\mathrm{Y}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},$ and ${\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ show insulator-metal transitions on the passage of small electrical currents. That such an electric-field-induced transition occurs even in ${\mathrm{Y}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ where the charge-ordered state is not affected by magnetic fields is noteworthy. The transition is attributed to the depinning of the randomly pinned charge solid. These materials also exhibit an interesting memory effect probably due to the randomness of the strength as well as the position of the pinning centers.