Measurements of polarized neutron scattering were performed on a S=1/2 chain multiferroic LiCu2O2. In the ferroelectric ground state with the spontaneous polarization along the c-axis, the existence of transverse spiral spin component in the bc-plane was confirmed. When the direction of electric polarization is reversed, the vector spin chirality as defined by Cij=Si×Sj (i and j being the neighboring spin sites) is observed to be reversed, indicating that the spin-current model or the inverse Dzyaloshinskii-Moriya mechanism is applicable even to this eg-electron quantum-spin system. Differential scattering intensity of polarized neutrons shows a large discrepancy from that expected for the classical-spin bc-cycloidal structure, implying the effect of large quantum fluctuation.
@article{arxiv.0801.2533,
title = {Correlation between spin helicity and electric polarization vector in quantum-spin chain magnet LiCu$_2$O$_2$},
author = {S. Seki and Y. Yamasaki and M. Soda and M. Matsuura and K. Hirota and Y. Tokura},
journal= {arXiv preprint arXiv:0801.2533},
year = {2009}
}