Relaxation dynamics in the one-dimensional organic charge-transfer salt \delta-(EDT-TTF-CONMe$_2$)$_2$Br

TL;DR

This study investigates the relaxation dynamics in a one-dimensional organic charge-transfer salt, revealing three relaxational processes including glassy freezing and excitations of a Wigner lattice, through thermal-expansion and dielectric spectroscopy.

Contribution

It provides the first detailed analysis of multiple relaxational processes in elta-(EDT-TTF-CONMe2)2Br, highlighting glassy freezing and Wigner lattice excitations distinct from related salts.

Findings

Glassy freezing of ethylene groups at low temperature.

Identification of Wigner lattice excitations via dielectric spectroscopy.

Distinct temperature behaviors for different relaxational processes.

Abstract

A detailed investigation of the charge-ordered charge-transfer salt \delta-(EDT-TTF-CONMe$_{2}$)$_{2}$Br by thermal-expansion measurements and dielectric spectroscopy reveals three dynamic processes of relaxational character. The slowest one exhibits the characteristics of glassy freezing and is ascribed to the conformational dynamics of terminal ethylene groups of the organic molecules. Such a process was previously found for related charge-transfer salts where, however, the anions form polymerlike chains, in contrast to the spherical anions of the present material. Dielectric spectroscopy reveals two additional relaxational processes. The characteristics of the faster one are consistent with excitations of a one-dimensional Wigner lattice as recently observed in this material by infrared spectroscopy, which are also accompanied by conformational changes of the molecules. However, at low temperature the ethylene-group relaxation exhibits the cooperativity-induced dramatic slowing down that is typical for glassy freezing, while the defect-related Wigner-lattice excitation follows thermally activated behavior as expected for single-dipole relaxations.