Magnetic field-driven transition between valence bond solid and antiferromagnetic order in distorted triangular lattice

TL;DR

This study demonstrates how an external magnetic field can induce a transition from a valence bond solid to antiferromagnetic order in a distorted triangular lattice molecular insulator, revealing quantum spin liquid characteristics.

Contribution

It uncovers the magnetic field-driven transition mechanism between valence bond solid and antiferromagnetic states in a distorted triangular lattice, highlighting the role of spin-lattice coupling.

Findings

Magnetic field suppresses valence bond order above 8 T.

Persistent antiferromagnetic correlations indicate a quantum spin liquid state.

Field-induced transition involves renormalized one-dimensionality and spin-lattice effects.

Abstract

A molecular Mott insulator $\kappa$-(ET)$_2$B(CN)$_4$ [ET = bis(ethylenedithio)tetrathiafulvalene] with a distorted triangular lattice exhibits a quantum disordered state with gapped spin excitation in the ground state. $^{13}$C nuclear magnetic resonance, magnetization, and magnetic torque measurements reveal that magnetic field suppresses valence bond order and induces long-range magnetic order above a critical field $\sim 8$ T. The nuclear spin-lattice relaxation rate $1/T_1$ shows persistent evolution of antiferromagnetic correlation above the transition temperature, highlighting a quantum spin liquid state with fractional excitations. The field-induced transition as observed in the spin-Peierls phase suggests that the valence bond order transition is driven through renormalized one-dimensionality and spin-lattice coupling.