Enhanced tunneling electroresistance in multiferroic tunnel junctions due to the reversible modulation of orbitals overlap

We report a first-principles study of the ferroelectricity and spin-dependent transport through Co/BaTiO3/CoO/Co multiferroic tunnel junctions (MFTJs). We find the coexistence of large tunneling magnetoresistance (TMR) ratio and large tunneling electroresistance (TER) ratio in the MFTJs. The large TMR effect originates from the spin-filter tunneling through the BaTiO3 barrier, while the TER effect is due to the modulation of orbitals overlap by polarization reversal. The microscopic physics of TER are identified and understood through the analysis of metal-oxygen relative displacements, local polarization magnitude, transmission in momentum space and real space scattering states. Our results provide a practical way to achieve the coexistence of large TER and TMR effects in MFTJs.