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

Yasuhiro Shimizu,Hideki Yamochi,Yukihiro Yoshida,Masayuki Itoh,Makoto Yoshida,Mitsuhiko Maesato,Genta Kawaguchi,David Graf,Akihiro Otsuka,Gunzi Saito,Masashi Takigawa

doi:10.1103/physrevresearch.3.023145

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.

Highlights

Quantum magnets featured by macroscopic quantum entanglements host exotic quasiparticles and topological order [1,2,3]
A molecular Mott insulator κ-(ET)2B(CN)4 [ET = bis(ethylenedithio)tetrathiafulvalene] with a distorted triangular lattice exhibits a quantum disordered state with gapped spin excitation in the ground state. 13C 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 ∼8 T
Tc = 5 K, χ measured at 1 T decreases continuously, indicating the second-order phase transition

Summary

Introduction

Quantum magnets featured by macroscopic quantum entanglements host exotic quasiparticles and topological order [1,2,3]. A valence bond order state with translational symmetry breaking competes with the magnetic order and quantum spin liquid states [4,5,6,7]. Under an intense magnetic field, the valence bond order state is destabilized and exhibits a transition into long-rangeorder states [12,13]. The fieldinduced transition involving long-range order of transverse magnetization is regarded as Bose-Einstein condensation of triplons, as observed in several quantum magnets [12,13,14,15,16,17,18,19,20].

Results

Discussion

Conclusion