Spin Liquid State in an Organic Mott Insulator with a Triangular Lattice

Abstract

[Formula presented] NMR and static susceptibility measurements have been performed in an organic Mott insulator with a nearly isotropic triangular lattice, [Formula presented], which is a model system of frustrated quantum spins. The static susceptibility is described by the spin [Formula presented] antiferromagnetic triangular-lattice Heisenberg model with the exchange constant [Formula presented]. Regardless of the large magnetic interactions, the [Formula presented] NMR spectra show no indication of long-range magnetic ordering down to 32 mK, which is 4 orders of magnitude smaller than [Formula presented]. These results suggest that a quantum spin liquid state is realized in the close proximity of the superconducting state appearing under pressure. © 2003 The American Physical Society.