Critical Spin Liquid versus Valence Bond Glass in Triangular Lattice Organic $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$

Abstract

In the quest for materials with unconventional quantum phases, the organic triangular-lattice antiferromagnet $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$ has been extensively discussed as a quantum spin liquid (QSL) candidate. Recently, an intriguing quantum critical behaviour was suggested from low-temperature magnetic torque experiments. Through microscopic analysis of all anisotropic contributions, including Dzyaloshinskii-Moriya and multi-spin scalar chiral interactions, we highlight significant deviations of the experimental observations from a quantum critical scenario. Instead, we show that disorder-induced spin defects provide a comprehensive explanation of the low-temperature properties. These spins are attributed to valence bond defects that emerge spontaneously as the QSL enters a valence bond glass phase at low temperature. This theoretical treatment is applicable to a general class of frustrated magnetic systems and has important implications for the interpretation of magnetic torque, nuclear magnetic resonance, thermal transport and thermodynamic experiments.

v3 includes improved readability with several additional comments and a more detailed discussion of the origin and consequences of local moments

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• The 2021 Quantum Materials Roadmap
• Four-Spin Terms and the Origin of the Chiral Spin Liquid in Mott Insulators on the Triangular Lattice
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• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Thermodynamic and Transport Properties in Disordered Kitaev Models
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• A $j_{\mathrm{eff}}=1/2$ Kitaev material on the triangular lattice: The case of NaRuO${}_2$
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• Two-Particle Self-Consistent method for the multi-orbital Hubbard model
• Quantum-critical scaling properties of the two-dimensional random-singlet state
• Effects of spin-phonon coupling in frustrated Heisenberg models
• Charge disproportionation in the spin-liquid candidate $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$ at 6 K revealed by ${}^{63}$Cu NQR measurements
• Ingredients for Generalized Models of $\kappa$-Phase Organic Charge-Transfer Salts: A Review
• Magnetic ground states in kagome YCu${}_3$(OH)${}_6$[(Cl${}_x$Br${}_{1-x}$)${}_{3-y}$(OH)${}_y$]
• Variational wave functions for the spin-Peierls transition in the Su-Schrieffer-Heeger model with quantum phonons
• Improved effective vertices in the multi-orbital Two-Particle Self-Consistent method from Dynamical Mean-Field Theory
• Ferromagnetism out of charge fluctuation of strongly correlated electrons in $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Br
• Spin Vortex Crystal Order in Organic Triangular Lattice Compound
• Coherent heavy charge carriers in an organic conductor near the bandwidth-controlled Mott transition
• Spin- and Flux-gap Renormalization in the Random Kitaev Spin Ladder
• Chasing the spin gap through the phase diagram of a frustrated Mott insulator
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• Disorder-induced excitation continuum in a spin-1/2 cobaltate on a triangular lattice
• Thermodynamic Properties of the Mott Insulator-Metal Transition in a Triangular Lattice System Without Magnetic Order
• Charge and spin interplay in a molecular-dimer-based organic Mott insulator
• Destabilization of U(1) Dirac spin-liquids on two dimensional non-bipartite lattices by quenched disorder
• Non-equilibrium magnetic response in concentrated spin-glass AuFe(11%) alloy
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• Exploration of magnetoelastic deformations in spin-chain compound CuBr${}_2$
• Lattice dynamics of the frustrated kagome compound Y-kapellasite
• Gapped magnetic ground state in the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Ag${}_2$(CN)${}_3$ suggested by magnetic spectroscopy
• Magnetic interactions of 4$f$ electrons in the topological insulator chalcogenide Bi${}_2$Se${}_3$
• Electronic correlations and spin frustration in the molecular conductors $\kappa$-(BEDT-TTF)${}_2$X probed by magnetic quantum oscillations
• Electronic properties of the dimerized organic conductor $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$
• Reentrance of metal-insulator transition and magnetic competitions on a triangular lattice with second nearest-neighbor hopping
• Charge-Transfer Complex $\kappa$-(BEST)${}_2$Cu${}_2$(CN)${}_3$ Analogous to Organic Spin Liquid Candidate
• ESR Investigations of the Magnetic Anisotropy in $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$
• ${}^{13}$C NMR observation of a nonmagnetic charge-ordered state in the organic conductor $\kappa$-(ET)${}_2$Hg(SCN)${}_2$Cl