Natalia DRICHKO
Mott insulators are commonly pictured with electrons localized on lattice sites, with their low-energy degrees of freedom involving spins only. Mott insulators based on dimers if BEDT-TTD-type molecules have shown a possibility to additionally host an electric dipole on a dimer lattice site when the charge inversion symmetry on a dimer is broken. It creates a unique situation where electric dipole and spin degree of freedom originate from the same electrons. A static order of electric dipoles can lead to a ferroelectric spin singlet state. Frustrated triangular lattice of dimers of BEDT-TTF and similar molecules can host a spin liquid state, while frustrated lattice of electric dipoles was predicted to produce dipole liquid, where fluctuations of electric dipoles coupled to spins result in a spin liquid state. Using Raman scattering spectroscopy as the main experimental technique, we follow a range of kappa-phase materials based on BEDT-TTF molecule where charge degree of freedom activates and suppresses magnetic excitation spectrum characteristic for triangular lattice S=1/2 antiferromagnets. We observe fluctuating electric dipoles and re-entrant charge order transition for materials close to the transition into ferroelectric state. In the vicinity of the phase border the competing degrees of freedom result in inhomogeneities of the charge fluctuating system, which produces ferromagnetic-like response in magnetic susceptibility.