Imaging phase separation near the Mott boundary in the correlated organic superconductors $\kappa$-(BEDT-TTF)$_{2}$X

TL;DR

This study visualizes macroscopic electronic phase separation in a organic Mott system near the transition temperature, revealing a different scale of inhomogeneity compared to inorganic Mott materials.

Contribution

It reports direct imaging of large-scale metallic and insulating domains in an organic Mott insulator, highlighting a distinct class of electronic inhomogeneity.

Findings

Electronic phase separation occurs below 40 K.

Domains are 50-100 μm in size.

Different from nano-scale in inorganic Mott systems.

Abstract

Electronic phase separation consisting of the metallic and insulating domains with 50 -- 100 $\mu$m in diameter is found in the organic Mott system $\kappa$-[($h$8-BEDT-TTF)$_{1-x}$($d$8-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears below the critical end temperature 35 -- 40 K of the first order Mott transition. The observation of the macroscopic size of the domains indicates a different class of the intrinsic electronic inhomogeneity from the nano-scale one reported in the inorganic Mott systems such as High-$T_{c}$ copper and manganese oxides.