Antiferromagnetic ordering in organic conductor $\lambda$-(BEDT-TTF)$_2$GaCl$_4$ probed by $^{13}$C NMR

TL;DR

This study investigates the antiferromagnetic ground state of the organic conductor $$-(BEDT-TTF)$_2$GaCl$_4$ using magnetic susceptibility and $^{13}$C NMR, revealing AF correlations, a transition at 13 K, and its potential relation to superconductivity.

Contribution

The paper provides the first detailed NMR evidence of antiferromagnetic ordering in $$-(BEDT-TTF)$_2$GaCl$_4$, identifying it as an AF dimer-Mott insulator and linking it to the phase diagram of $$-type salts.

Findings

Antiferromagnetic correlation with $J/k_B \u2265 98$ K.

AF transition at approximately 13 K.

Ground state identified as AF dimer-Mott insulator.

Abstract

The ground state of $\lambda$-(BEDT-TTF)$_2$GaCl$_4$, which has the same structure as the organic superconductor $\lambda$-(BETS)$_2$GaCl$_4$, was investigated by magnetic susceptibility and $^{13}$C NMR measurements. The temperature dependence of the magnetic susceptibility revealed an antiferromagnetic (AF) correlation with $J/k_{\rm B} \simeq$ 98 K. NMR spectrum splitting and the divergence of $1/T_1$ were observed at approximately 13 K, which is associated with the AF transition. We found that the AF structure is commensurate according to discrete NMR peak splitting, suggesting that the ground state of $\lambda$-(BEDT-TTF)$_2$GaCl$_4$ is an AF dimer-Mott insulating state. Our results suggest that the superconducting phase of $\lambda$-type salts would be located near the AF insulating phase.