Unveiling the microscopic nature of correlated organic conductors: the case of kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x

TL;DR

This study combines first-principles calculations with dynamical mean field theory to uncover the microscopic electronic phases in organic conductors, revealing how electronic correlations influence optical properties and phase behavior.

Contribution

It introduces a novel approach combining DFT and DMFT tailored for organic systems to analyze their electronic phases and optical transitions.

Findings

Correlations are responsible for key optical features.

Some optical transitions are unaffected by correlations.

Insights into the phase diagram of organic conductors.

Abstract

A few organic conductors show a diversity of exciting properties like Mott insulating behaviour, spin liquid, antiferromagnetism, bad metal or unconventional superconductivity controlled by small changes in temperature, pressure or chemical substitution. While such a behaviour can be technologically relevant for functional switches, a full understanding of its microscopic origin is still lacking and poses a challenge in condensed matter physics since these phases may be a manifestation of electronic correlation. Here we determine from first principles the microscopic nature of the electronic phases in the family of organic systems kappa-(ET)2Cu[N(CN)2]BrxCl1-x by a combination of density functional theory calculations and the dynamical mean field theory approach in a new form adapted for organic systems. By computing spectral and optical properties we are able to disentangle the origin of the various optical transitions in these materials and prove that correlations are responsible for relevant features. Remarkably, while some transitions are inherently affected by correlations, others are completely uncorrelated. We discuss the consequences of our findings for the phase diagram in these materials.