Antiferromagnetic ordering of organic Mott insulator $\lambda$-(BEDSe-TTF)$_2$GaCl$_4$

TL;DR

This study investigates the magnetic and electronic properties of the organic Mott insulator $mbda$-(BEDSe-TTF)$_2$GaCl$_4$, revealing antiferromagnetic order and structural similarities to related compounds, advancing understanding of bandwidth-controlled organic conductors.

Contribution

The paper provides the first detailed analysis of the magnetic ordering and electronic structure of $mbda$-(BEDSe-TTF)$_2$GaCl$_4$, demonstrating its antiferromagnetic state and its relation to similar compounds.

Findings

$mbda$-BEDSe exhibits antiferromagnetic order below 22 K.

Structural and magnetic properties are similar to $mbda$-ET, indicating a common electronic phase.

The compound's $U/W$ ratio suggests strong electron correlation comparable to other Mott insulators.

Abstract

The band structure and magnetic properties of organic charge-transfer salt $\lambda$-(BEDSe-TTF)$_2$GaCl$_4$ (BEDSe-TTF: bis(ethylenediseleno)tetrathiafulvalene; abbreviated as $\lambda$-BEDSe) are investigated. The reported crystal structure is confirmed using X-ray diffraction measurements, and the transfer integrals are calculated. The degree of electron correlation $U/W$ ($U$: on-site Coulomb repulsion, $W$: bandwidth) of $\lambda$-BEDSe is larger than one and comparable to that of the isostructural Mott insulator $\lambda$-(ET)$_2$GaCl$_4$ (ET: bis(ethylenedithio)tetrathiafulvalene, abbreviated as $\lambda$-ET), whereas the $U/W$ of the superconducting salt $\lambda$-(BETS)$_2$GaCl$_4$ (BETS: bis(ethylenedithio)tetraselenafulvalene) is smaller than one. $^{13}$C-NMR and $\mu$SR measurements revealed that $\lambda$-BEDSe undergoes an antiferromagnetic (AF) ordering below $T_{\rm N} = 22$~K. In the AF state, discrete $^{13}$C-NMR spectra with a remaining central peak are observed, indicating the commensurate AF spin structure also observed in $\lambda$-ET. The similarity between the structural and magnetic properties of $\lambda$-BEDSe and $\lambda$-ET suggests that both salts are in the same electronic phase, i.e., the physical properties of $\lambda$-BEDSe can be understood by the universal phase diagram of bandwidth-controlled $\lambda$-type organic conductors obtained by donor molecule substitution.