Effect of polar interfaces on thin-film ferroelectricity

Based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics [1]. We consider Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and SrRuO3/LaO/BaTiO3/LaO heterostructures as representative systems, where a LaO monolayer at the interface with a TiO2-terminated BaTiO3 produces a polar interface. The polar interfaces create an intrinsic electric field which produces electric polarization in BaTiO3 directed into the interior of the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. The effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces. [1] Y. Wang et al., Phys. Rev. B. 82, 094114 (2010).