Quantum Fluctuations of Chirality in One-Dimensional Spin-1/2 Multiferroics: Gapless Dielectric Response from Phasons and Chiral Solitons

We present a quantum theory for one-dimensional spin-1/2 multiferroics, where the vector spin chirality couples with the electric polarization. Based on exact diagonalization and bosonization, it is shown that quantum fluctuations appreciably reduce the chiral ordering amplitude and the associated ferroelectric polarization. This yields nearly collinear spin correlations in short-range scales, in qualitative agreement with recent neutron scattering experiments. There appear gapless chirality excitations described by phasons and new solitons, which can be experimentally verified from the low-energy dielectric response.