Multiferroic behavior in trimerized Mott insulators

We demonstrate multiferroic behavior in trimerized Mott insulators through the interplay between spins and electric dipole moments resulting from electronic charge fluctuations in frustrated units [L. N. Bulaevskii, C. D. Batista, M. V. Mostovoy, and D. I. Khomskii, Phys. Rev. B 78, 024402 (2008)]. The model consists of stacked triangular layers of trimers with small inter-trimer exchange interactions $J'$ and $J''$. We construct a phase diagram using a semi-classical approach. Ferroelectric states coexist with ferro- or antiferromagnetic orderings depending on the value of the magnetic field $H$ and the sign of the inter-layer exchange $J''$. The electric polarization undergoes abrupt changes as a function of $H$.