We examine the electronic properties of newly discovered ferroelectric metal LiOsO$_3$ combining density-functional and dynamical mean-field theories. We show that the material is close to a Mott transition and that electronic correlations can be tuned to engineer a Mott multiferroic state in 1/1 superlattice of LiOsO$_3$ and LiNbO$_3$. We use electronic structure calculations to predict that the (LiOsO$_3$)$_1$/(LiNbO$_3$)$_1$ superlattice is a type-I multiferroic material with a ferrolectric polarization of 41.2~$mu$C cm$^{-2}$, Curie temperature of 927,K, and Neel temperature of 671,K. Our results support a route towards high-temperature multiferroics, emph{i.e.}, driving non-magnetic emph{polar metals} into correlated insulating magnetic states.
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