  Interfaces in oxide heterostructures always provide a fertile ground for
emergent properties. Charge transfer from a high energy band to a low energy
opponent is naturally expected, as occurring in semiconductor $p$-$n$
junctions. In this study, several exceptional physical phenomena have been
predicted in (YFeO$_3$)$_n$/(YTiO$_3$)$_n$ superlattices. First, the charge
transfer between these Mott insulators is in opposite to the intuitive band
alignment scenario. Second, hybrid ferroelectricity with a moderate
polarization is generated in the $n=2$ magnetic superlattice. Furthermore, the
ferroelectric-type distortion can persist even if the
($AB$O$_3$)$_2$/($AB$'O$_3$)$_2$ system turns to be metallic, rending possible
metallic ferroelectricity.
