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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 11: Focus Session: (Multi-)Ferroic States II

KFM 11.4: Talk

Tuesday, March 19, 2024, 10:40–11:00, EMH 225

Interplay of layer and spontaneous polarization in superlattices of metallic SmNiO₃ and ferroelectric BaTiO₃ — •Edith Simmen and Nicola A. Spaldin — Materials Theory, ETH Zurich, Switzerland

We present a density functional theory (DFT) study of superlattices containing metallic SmNiO₃ (SNO) and ferroelectric BaTiO₃ (BTO). The interface of SNO with BTO hosts numerous interesting functionalities which can compete or cooperate: Since BTO and SNO are II-IV and III-III perovskites, respectively, the different layer charges lead to a built-in polar discontinuity in addition to the spontaneous polarization of BTO. These two sources of polarization can both interact with each other and with the SNO via its metallic screening. We find that despite the metallicity of SNO, the polar electrostatics strongly affect the ground state. The system avoids a polar discontinuity by aligning the spontaneous polarization of the BTO parallel to the layer polarization of the SNO in the so-called ‘happy’ orientation. We find that this happy polarization is stable down to a single unit cell of BTO, in contrast to the 6-unit-cell critical thickness previously found for BTO with II-IV metallic electrodes [1]. The opposite ‘unhappy’ polarization orientation is however highly unfavoured, with the stability depending strongly on the thickness of the BTO layer and the tilts within the SNO layer.
[1] J. Junquera et al., Nature 422, 506 (2003)

Keywords: ferroelectricity; polar discontinuity; density functional theory; layer polarization; metallic screening