  The polarity-dependent resistive-switching across metal-Pr0.7Ca0.3MnO3
interfaces is investigated. The data suggest that shallow defects in the
interface dominate the switching. Their density and fluctuation, therefore,
will ultimately limit the device size. While the defects generated/annihilated
by the pulses and the associated carrier depletion seem to play the major role
at lower defect density, the defect correlations and their associated hopping
ranges appear to dominate at higher defect density. Therefore, the switching
characteristics, especially the size-scalability, may be altered through
interface treatments.
