Anions effects on the electronic structure and electrodynamic properties of the Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_{3}$

TL;DR

This study investigates how anions influence the electronic and electrodynamic properties of a Mott insulator with a quantum-spin-liquid state, revealing charge imbalance, relaxor behavior, and domain wall excitations.

Contribution

It uncovers the role of anions in supporting valence bands and inducing electronic configurations that lead to glassy dynamics in spin-liquid Mott insulators.

Findings

Charge imbalance between inequivalent sites.

Presence of relaxor dielectric response.

Glassy dynamics from charged domain walls.

Abstract

The Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ forms a highly-frustrated triangular lattice of $S=1/2$ dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasi-degenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$.