Spin Liquid State in an Organic Mott Insulator with Triangular Lattice

TL;DR

This study provides evidence for a quantum spin liquid state in an organic triangular-lattice Mott insulator, showing no magnetic order down to very low temperatures despite strong magnetic interactions.

Contribution

It demonstrates the realization of a quantum spin liquid in an organic Mott insulator with a nearly isotropic triangular lattice, a significant step in understanding frustrated quantum spin systems.

Findings

No magnetic ordering observed down to 32 mK

Susceptibility matches triangular-lattice Heisenberg model

Quantum spin liquid state likely near superconductivity

Abstract

$^{1}$H NMR and static susceptibility measurements have been performed in an organic Mott insulator with nearly isotropic triangular lattice, $\kappa$-(BEDT-TTF)$_{2}$Cu$_{2}$(CN)$_{3}$, which is a model system of frustrated quantum spins. The static susceptibility is described by the spin $S$ = 1/2 antiferromagnetic triangular-lattice Heisenberg model with the exchange constant $J$ $\sim$ 250 K. Regardless of the large magnetic interactions, the $^{1}$H NMR spectra show no indication of long-range magnetic ordering down to 32 mK, which is four-orders of magnitude smaller than $J$. These results suggest that a quantum spin liquid state is realized in the close proximity of the superconducting state appearing under pressure.