Anomalous dielectric response in the dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$

TL;DR

This study investigates the dielectric properties of the dimer Mott insulator $$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, revealing quantum dipole behavior and charge disproportionation that suggest complex charge dynamics in a spin-liquid state.

Contribution

It uncovers nontrivial charge degrees of freedom and quantum mechanical dipoles in a well-known spin-liquid organic insulator, expanding understanding of its dielectric response.

Findings

Detection of dipole-glass-like dielectric relaxation below 60 K

Charge disproportionation within dimers due to Coulomb interactions

Observation of quantum mechanical dipoles with unexpected responses

Abstract

We have measured and analyzed the dielectric constant of the dimer Mott insulator $\kappa-$(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, which is known as a playground for a spin-liquid state. Most unexpectedly, this particular organic salt has nontrivial charge degrees of freedom, being characterized by a dipole-glass-like dielectric relaxation below around 60 K. This is ascribed to the charge disproportionation within the dimer due to the intersite Coulomb repulsion. In this respect, the dipole observed here is purely quantum mechanical, and thereby exhibits unexpected responses.