Interface Control of Emergent Ferroic Order in Ruddlesden-Popper Srn+1TinO3n+1

We discovered from first principles an unusual polar state in the low n Srn+1TinO3n+1 Ruddlesden-Popper (RP) layered perovskites in which ferroelectricity is nearly degenerate with antiferroelectricity, a relatively rare form of ferroic order. We show that epitaxial strain plays a key role in tuning the perpendicular coherence length of the ferroelectric mode, and does not induce ferroelectricity in these low-dimensional RP materials as is well known to occur in SrTiO3. These systems present an opportunity to manipulate the coherence length of a ferroic distortion in a controlled way, without disorder or a free surface.