  The ferroelectric (FE) control of electronic transport is one of the emerging
technologies in oxide heterostructures. Many previous studies in FE tunnel
junctions (FTJs) exploited solely the differences in the electrostatic
potential across the FTJs that are induced by changes in the FE polarization
direction. Here, we show that in practice the junction current ratios between
the two polarization states can be further enhanced by the electrostatic
modification in the correlated electron oxide electrodes, and that FTJs with
nanometer thin layers can effectively produce a considerably large
electroresistance ratio at room temperature. To understand these surprising
results, we employed an additional control parameter, which is related to the
crossing of electronic and magnetic phase boundaries of the correlated electron
oxide. The FE-induced phase modulation at the heterointerface ultimately
results in an enhanced electroresistance effect. Our study highlights that the
strong coupling between degrees of freedom across heterointerfaces could yield
versatile and novel applications in oxide electronics.
