Engineering ferroelectrics and magnetoelectrics in low dimensional interfaces

Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. In this project we study the emergence of  ferroelectricity in artificial tri-layer superlattices consisting solely of non-ferroelectric layers. Recently we observed emergent ferroelectricity below 40 K in superlattices composed of three different antiferromagnetic insulating manganites NdMnO₃/SrMnO₃/LaMnO₃. The system also exhibited strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of the polarization. Density functional calculations indicated that broken space inversion symmetry and mixed valency, because of cationic asymmetry and interfacial polar discontinuity, respectively, gave rise to the observed behaviour. Our results demonstrate the engineering of asymmetric layered structures with emergent ferroelectric and magnetic field tunable functions distinct from that of normal devices, for which the components are typically ferroelectrics. We are now working towards enriching the list of materials exhibiting the abovementioned properties aiming at improving performance and versatility.