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

TL;DR

This study uses density functional theory with spin-orbit coupling to analyze the origin of ferroelectricity in spiral magnets LiCu2O2 and LiCuVO4, revealing the key role of spin-orbit coupling and atom-specific contributions to electric polarization.

Contribution

It provides a detailed first-principles analysis of the microscopic mechanisms behind multiferroicity in these cuprates, highlighting the importance of spin-orbit coupling and atomic density distributions.

Findings

Spin-orbit coupling on Cu sites drives ferroelectricity.

Electric polarization is larger in the ab-plane spin spiral.

The model explains the polarization direction in LiCuVO4 but not in LiCu2O2.

Abstract

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- 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.