Density-Functional Characterization of the Multiferroicity in Spin Spiral Chain Cuprates

The ferroelectricity of the spiral magnets LiCu₂O₂ and LiCuVO₄ was examined by calculating the electric polarizations of their spin spiral states on the basis of density-functional theory with spin-orbit coupling. Our work unambiguously reveals that spin-orbit coupling is responsible for the ferroelectricity with the primary contribution from the spin-orbit coupling on the Cu sites, but the asymmetric density distribution responsible for the electric polarization occurs mainly around the O atoms. The electric polarization is calculated to be much greater for the ab-plane than for the bc-plane spin spiral. The observed spin-spiral plane is found to be consistent with the observed direction of the electric polarization for LiCuVO₄, but inconsistent for LiCu₂O₂.

©2007 The American Physical Society