Multiferroic Pr$_2$Ti$_2$O$_7$: A candidate material to search for the electric dipole moment of the electron

We use density functional theory (DFT) to explore the suitability of the A$_n$B$_n$O$_{3n+2}$ perovskite oxides [1] as materials for searching for the electric dipole moment (eEDM). The experimental search for the eEDM is of interest as its observation would confirm the violation of charge-parity (CP) symmetry in the Universe. Experiments involving electric-field-correlated measurements in solids are promising. In particular, multiferroic Eu$_{0.5}$Ba$_{0.5}$TiO$_3$, which was designed specifically to search for the eEDM, set an improved limit compared with previous solid-state searches [2], but suffered from hysteretic heating [3]. Here we show that the A$_n$B$_n$O$_{3n+2}$ layered perovskites ($n=4$, A=Pr,Gd and B=Ti) have an alternative mechanism for ferroelectricity plus appropriate magnetic interactions, suggesting that they are suitable candidates for an eEDM search. [1] F. Lichtenberg, A. Herrnberger, K. Wiedenmann, Prog. Solid State Chem. \textbf{36} (2008). [2] K.Z. Rushchanskii, S. Kamba, V. Goian, \textit{et al.}, Nature Mater. \textbf{9}, 649 (2010). [3] S. Eckel, A.O. Sushkov, and S.K. Lamoreaux, Phys. Rev. Lett. \textbf{109}, 193003, (2012).