Phonon renormalization effects accompanying the 6 K anomaly in the quantum spin liquid candidate Κ-(BEDT-TTF)2Cu2(CN)3

The low-temperature state of the quantum spin liquid candidate K-(BEDT-TTF)2Cu2(CN)3 emerges via an anomaly at T* ti 6 K. Although signatures of this anomaly have been revealed in various quantities, its origin has remained unclear. Here we report inelastic neutron scattering measurements on single crystals of K-(BEDT-TTF)2Cu2(CN)3, aiming at studying phonon renormalization effects at T*. A drastic change was observed in the phonon damping across T* for a breathing mode of BEDT-TTF dimers at E = 4.7 meV. The abrupt change in the phonon damping is attributed to a phase transition into a valence bond solid state based on an effective model describing the spin-charge coupling in this dimer-Mott system.

Automated summary

The low-temperature state of the quantum spin liquid candidate K-(BEDT-TTF)2Cu2(CN)3 undergoes an anomaly at T*, which is revealed by the drastic change in phonon damping. This change is attributed to a phase transition into a valence bond solid state based on an effective model describing the spin-charge coupling in this system.