Jahn-Teller distortions as a novel source of multiferroicity

The Jahn-Teller effect is a fascinating and ubiquitous phenomenon in modern quantum physics and chemistry. We propose a class of oxides with a melilite structure Ba sub(2) T Ge sub(2) O sub(7) (T = V, Ni) where Jahn-Teller distortions are mainly responsible for the appearance of electric polarization. At the heart of the proposed mechanism lies the lack of inversion symmetry displayed by tetrahedrally coordinated transition-metal ions, which allows for the condensation of polar Jahn-Teller distortions, at odds with octahedral coordination typical of conventional ferroelectric oxides with a perovskite structure. Since the noncentrosymmetric local environment of transition-metal ions also activates the proposed spin-dependent hybridization mechanism for magnetically induced electric polarization, proper multiferroic phases with intrinsic magnetoelectric interactions could be realized in this class of low-symmetry materials.