Abstract
Inelastic neutron scattering measurements on the molecular dimer-Mott insulator reveal a phonon anomaly in a wide temperature range. Starting from where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature , where also a ferroelectric ordering at occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below , while no change of the lattice symmetry is observed across 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.
- Received 28 December 2018
- Revised 24 May 2019
DOI:https://doi.org/10.1103/PhysRevLett.123.027601
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