Domain-wall ferroelectric tunnel junction with triple resistance states

The tunneling electroresistance (TER) effect in ferroelectric tunnel junctions (FTJs) has attracted interest due to potential applications in non-volatile memory devices. TER represents dramatic change in resistance of FTJ upon polarization reversal in ferroelectric barrier. A new type of TER's proposed, utilizing a head-to-head ferroelectric domain wall in La_1-xSr_xMnO₃(LSMO)/BaTiO₃(BTO)/LSMO FTJ with the wall parallel to the plane. Domain wall state has higher conductance than uniformly polarized states, but is metastable and thus not reversible. This work, using first-principles DFT calculations, explores stability of the wall in this FTJ, by considering different La_1-xSr_xO/TiO₂ terminations at LSMO/BTO interfaces. Due to polar nature of the interface, appearance of the wall depends on doping level x. For x<0.4 domain wall state becomes global minimum, and DFT calculations demonstrate a triple-well energy profile with respect to net polarization. Using an electric field, the FTJ can be switched reversibly between domain wall and two uniformly polarized states. Using a phenomenological model based on Landau-Devonshire free energy and parameters obtained from DFT calculations, we analyze the hysteresis loops of this FTJ demonstrating the emergence of the triple resistance states.