  Single crystals of Nd0.5Ca0.5MnO3 and Pr0.6Ca0.4MnO3 show current-induced
insulator-metal transitions at low temperatures. In addition, the
charge-ordering transition temperature decreases with increasing current. The
electroresistive ratio, defined as r0.5/rI where r0.5 is the resistivity at a
current of 0.5 mA and rI the resistivity at a given applied current, I, varies
markedly with temperature and the value of I. Thermal hysteresis observed in
Nd0.5Ca0.5MnO3 and Pr0.6Ca0.4MnO3 at the insulator-metal transition indicates
that the transition is first-order. The current-induced changes are comparable
to those induced by magnetic fields, and the insulator-metal transition in
Pr0.6Ca0.4MnO3 is accordingly associated with a larger drop in resistivity.
