Spin excitations of a proximate Kitaev quantum spin liquid realized in Cu${}_2$IrO${}_3$

Abstract

Magnetic moments arranged at the corners of a honeycomb lattice are predicted to form a novel state of matter, Kitaev quantum spin liquid, under the influence of frustration effects between bond-dependent Ising interactions. Some layered honeycomb iridates and related materials, such as Na${}_2$IrO${}_3$ and $\alpha$-RuCl${}_3$, are proximate to Kitaev quantum spin liquid, but bosonic spin-wave excitations associated with undesirable antiferromagnetic long-range order mask the inherent properties of Kitaev Hamiltonian. Here, we use ${}^{63}$Cu nuclear quadrupole resonance to uncover the low energy spin excitations in the nearly ideal honeycomb lattice of effective spin $S=1/2$ at the Ir${}^{4+}$ sites in Cu${}_2$IrO${}_3$. We demonstrate that, unlike Na${}_2$IrO${}_3$, Ir spin fluctuations exhibit no evidence for critical slowing down toward magnetic long range order in zero external magnetic field. Moreover, the low energy spin excitation spectrum is dominated by a mode that has a large excitation gap comparable to the Ising interactions, a signature expected for Majorana fermions of Kitaev quantum spin liquid.

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References in corpus (10)

• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Models and Materials for Generalized Kitaev Magnetism
• On the Origin of Zigzag Magnetic Order in Iridium Oxide Na2IrO3
• Scattering Continuum and Possible Fractionalized Excitations in $\alpha$-RuCl${}_3$
• Long range magnetic ordering in Na${}_2$IrO${}_3$
• ^{63}Cu, ^{35}Cl, and ^{1}H NMR in the S=1/2 Kagomé Lattice ZnCu_{3}(OH)_{6}Cl_{2}
• Effect of nonmagnetic dilution in honeycomb lattice iridates Na${}_2$IrO${}_3$ and Li${}_2$IrO${}_3$
• Local Spin Susceptibility of the S=1/2 Kagome Lattice in ZnCu3(OD)6Cl2
• Temperature evolution of spin dynamics in two- and three-dimensional Kitaev models: Influence of fluctuating gauge fluxes
• Evolution of Magnetism in the $N{a}_{3-d}N{a}_{1-x}M{g}_{x}I{r}_2{O}_6$ Series of Honeycomb Iridates

Cited by in corpus (17)

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• Impurity-induced resonant spinon zero modes in Dirac quantum spin-liquids
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• Controlling magnetic frustration in 1T-TaS${}_2$ via Coulomb engineered long-range interactions
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• Local probe investigation of the spin dynamics in the kagome and inter-layers of orthorhombic barlowite Cu${}_4$(OD)${}_6$FBr: ${}^{79}$Br and ${}^{63}$Cu NQR study