Real space imaging of the metal - insulator phase separation in the band width controlled organic Mott system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br

TL;DR

This study uses scanning micro-region infrared spectroscopy to visualize and analyze the phase separation between metallic and insulating regions in a bandwidth-controlled organic Mott system, revealing its dependence on chemical substitution.

Contribution

First real space imaging of phase separation in a bandwidth-controlled organic Mott system using synchrotron radiation.

Findings

Phase separation appears near the Mott boundary.

The metal-insulator fraction varies with substitution ratio.

The phenomenon aligns with the strongly correlated electronic phase diagram.

Abstract

Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal-insulator fraction with the substitution ratio $x$ in $\kappa$-[($h$-BEDT-TTF)$_{1-x}$($d$-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br, of which band width is controlled by the substitution ratio $x$ between the hydrogenated BEDT-TTF molecule ($h$-BEDT-TTF) and the deuterated one ($d$-BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.