# Semimetallic and charge-ordered $\alpha$-(BEDT-TTF)$_2$I$_3$: on the role of disorder in dc transport and dielectric properties

## TL;DR

This study investigates how disorder influences dc transport and dielectric properties in the charge-ordered and semimetallic phases of $ ext{α}$-(BEDT-TTF)$_2$I$_3$, revealing the roles of scattering, conduction channels, and dielectric behavior.

## Contribution

It provides a detailed analysis of transport mechanisms and dielectric response in $ ext{α}$-(BEDT-TTF)$_2$I$_3$, highlighting the impact of disorder and charge ordering.

## Key findings

- Semimetallic phase shows temperature-independent conductivity due to inter-pocket scattering.
- Charge-ordered phase exhibits dual conduction channels: activation and hopping.
- Disorder from anion layers affects dielectric properties and conduction mechanisms.

## Abstract

$\alpha$-(BEDT-TTF)$_2$I$_3$ is a prominent example of charge ordering among organic conductors. In this work we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly inter-pocket scattering which equalizes mobilities of the two types of charge carriers. At low temperatures, within the insulating charge-ordered phase two channels of conduction can be discerned: a temperature-dependent activation which follows the mean-field behavior, and a nearest-neighbor hopping contribution. Together with negative magnetoresistance, the latter relies on the presence of disorder. The charge-ordered phase also features a prominent dielectric peak which bears a similarity to relaxor ferroelectrics. Its dispersion is determined by free-electron screening and pushed by disorder well below the transition temperature. The source of this disorder can be found in the anion layers which randomly perturb BEDT-TTF molecules through hydrogen bonds.