# The metal-insulator transition in the organic conductor $\beta^{\prime\prime}$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Cl

## TL;DR

This study investigates the metal-insulator transition in an organic conductor using multiple spectroscopic and transport techniques, revealing gradual dimerization, charge ordering, and specific energy gaps associated with the transition.

## Contribution

It provides a comprehensive multi-technique analysis of the transition, highlighting the interplay of structural, magnetic, and electronic changes in the material.

## Key findings

- Gradual dimerization along the stacking direction at 150K
- Charge ordering develops at 72K with charge disproportionation of 0.34e
- Spin and charge gaps of 47meV and 60meV are identified

## Abstract

We explore the nature of the metal-insulator transition in $\beta^{\prime\prime}$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Cl by x-ray, electrical transport, ESR, Raman and infrared investigations. Magnetic and vibrational spectroscopy concurrently reveal a gradual dimerization along the stacking direction $a$, setting in already at the crossover temperature of 150K from the metallic to the insulating state. A spin gap $\Delta_\sigma = 47$meV is extracted. From the activated resistivity behavior below 55K a charge gap $\Delta_\rho=60$meV is derived. At $T_{\rm CO} = 72$K the C=C vibrational modes reveal the development of a charge-ordered state with a charge disproportionation of $2\delta_{\rho}=0.34e$