Ferroelectricity and New Quantum Magnetic States of Frustrated One-Dimensional Quantum Spin Systems

Abstract

Neutron scattering study and measurements of magnetic and dielectric properties have been studied for quasi one-dimensional spin 1/2 systems which are formed of edge-sharing CuO₄ square planes called CuO₂ ribbon chains. Due to the geometrical characteristic of the crystal structure of these systems, the nearest-neighbor exchange interaction between spins is ferromagnetic, and the second neighbor interaction is antiferromagnetic. The CuO₂ ribbon chain systems are typical examples for the frustrated quantum spin systems driven by the competing interactions. We found that LiVCuO₄ and PbCuSO₄(OH)₂ with CuO₂ ribbon chains have helical magnetic order and exhibit a ferroelectric transition with the magnetic transition, simultaneously (called multiferroic). For the CuO₂ ribbon chain systems, exotic quantum phases are theoretically predicted such as Haldane-dimer, spin-nematic, quadrupolar-order, and chiral-order phases. Rb₂Cu₂Mo₃O₁₂ with CuO₂ ribbon chains does not exhibit the long range ordering due to the quantum spin fluctuation and low dimensionality. For Rb₂Cu₂Mo₃O₁₂, the ferroelectric transition is found to be induced by applying field without magnetic transition, which is a new type ferroelectric transition triggered by the magnetism of frustrated quantum spin systems. The obtained results strongly suggest that Rb₂Cu₂Mo₃O₁₂ exhibits some exotic quantum states.