Charge and spin interplay in a molecular-dimer-based organic Mott insulator

TL;DR

This study investigates how charge and spin interactions influence magnetic properties in a specific organic Mott insulator, revealing charge-spin separation and coupling phenomena across different temperature regimes.

Contribution

It provides new insights into charge-spin interplay and phase transitions in a triangular lattice organic Mott insulator near charge order transition.

Findings

Charge and spin separation occur between 30K and 24K.

Charge and spin degrees of freedom couple below 24K.

Charge order melting prevents spin singlet state formation below 15K.

Abstract

Triangular lattice quasi-two-dimensional Mott insulators based on BEDT-TTF molecule and its analogies present a possibility to produce exotic phases by coupling charge and spin degrees of freedom. In this work we discuss magnetic properties of one of such materials, $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl, which is found at the border of the phase transition between a Mott insulator into a charge ordered state. Our magnetic susceptibility and cantilever magnetisation measurements demonstrate how the charge degree of freedom defines magnetic properties for few different charge phases observed in this material as a function of temperature. Between $T_{CO}=30~K$ and $T_S=24~K$ we observe charge and spin separation due to one-dimensional charge stripes formed in this material below $T_{CO}=30~K$. Below $T_S=24~K$ charge and spin degrees of freedom demonstrate coupling. Spin singlet correlations develop below 24~K, however melting of charge order below 15~K prevents the spin singlet state formation, leaving the system in the inhomogeneous state with charge ordered spin singlet domains and charge and spin fluctuating ones.