Magnetoelectric coupling in the multiferroic compound LiCu ₂O₂

We investigate the possible types of coupling between ferroelectricity and magnetism for the zigzag spin chain multiferroic compound LiCu2 O2. We construct a multi-order-parameter phenomenological model for the material based on a group theoretical analysis. We find that a theory involving interchain magnetoelectric coupling belonging to the same unit cell explains the experimental results of Park [Phys. Rev. Lett. 98, 057601 (2007)]. Our proposed model is able to relate the flop of the spin-spiral plane with the direction of the electric polarization. From our calculations we conclude that the zero-field structure observed by Seki [Phys. Rev. Lett. 100, 127201 (2004)] is the correct one. Furthermore, based on our theoretical model we make specific selection rule predictions about electromagnon excitations present in the LiCu2 O2 system. We predict that the electromagnon peaks measured in an ac-conductivity measurement are field dependent.