Persistence of fermionic spin excitations through a genuine Mott transition in $\kappa$-type organics

TL;DR

This study demonstrates that fermionic spin excitations persist through a genuine Mott transition in a $$-type organic system, revealing continuous evolution from a Fermi liquid to a quantum spin liquid with implications for understanding correlated electron phases.

Contribution

It provides experimental evidence that fermionic spin excitations survive a genuine Mott transition in an organic dimer-Mott system, challenging traditional views on electron localization.

Findings

Quantum Mott transition occurs around x=0.10 with BEDSe-TTF substitution.

Fermionic low-energy excitations remain in insulating salts after the transition.

Transition classified as a genuine Mott transition based on combined measurements.

Abstract

We investigate the continuous variation of electronic states from a Fermi liquid to a quantum spin liquid induced by chemical substitution in the organic dimer-Mott system of $\kappa$-[(BEDSe-TTF)$_x$(BEDT-TTF)$_{1-x}$]$_2$Cu[N(CN)$_2$]Br. Electrical transport measurements reveal that the mixing of BEDSe-TTF into the BEDT-TTF layers induces a quantum Mott transition around $x$=0.10. Although a charge gap disappears at this point, magnetic susceptibility and heat capacity measurements indicate that fermionic low-energy excitations remain in the insulating salts, suggesting that fermionic spin excitations persist. We propose that the transition can be classified into a genuine Mott transition.