Inelastic neutron scattering measurements on the molecular dimer-Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl reveal a phonon anomaly in a wide temperature range. Starting from Tins∼50-60 K where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature TN=27 K, where also a ferroelectric ordering at TFE≈TN occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below TN, while no change of the lattice symmetry is observed across TN in neutron diffraction measurements. We assign the phonon anomalies to structural fluctuations coupled to charge and spin degrees of freedom in the BEDT-TTF molecules.
ASJC Scopus subject areas
- Physics and Astronomy(all)