Majorana dynamical mean-field study of spin dynamics at finite temperatures in the honeycomb Kitaev model

Abstract

A prominent feature of quantum spin liquids is fractionalization of the spin degree of freedom. Fractionalized excitations have their own dynamics in different energy scales, and hence, affect finite-temperature ($T$) properties in a peculiar manner even in the paramagnetic state harboring the quantum spin liquid state. We here present a comprehensive theoretical study of the spin dynamics in a wide $T$ range for the Kitaev model on a honeycomb lattice, whose ground state is such a quantum spin liquid. In this model, the fractionalization occurs to break up quantum spins into itinerant matter fermions and localized gauge fluxes, which results in two crossovers at very different $T$ scales. Extending the previous study for the isotropic coupling case [J. Yoshitake, J. Nasu, and Y. Motome, Phys. Rev. Lett. $\text{1}17$, 157203 (2016)], we calculate the dynamical spin structure factor, the NMR relaxation rate, and the magnetic susceptibility while changing the anisotropy in the exchange coupling constants, by using the dynamical mean-field theory and the continuous-time quantum Monte Carlo method based on a Majorana fermion representation. We find that the system exhibits peculiar behaviors below the high-$T$ crossover whose temperature is comparable to the average of the exchange constants, reflecting the spin fractionalization in the paramagnetic region. Among them, the dichotomy between the static and dynamical spin correlations is unusual behavior hardly seen in conventional magnets. We discuss the relation between the dichotomy and the spatial configuration of gauge fluxes. Our results could stimulate further experimental and theoretical analyses of candidate materials for the Kitaev quantum spin liquids.

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• Thermodynamic and Transport Properties in Disordered Kitaev Models
• Spin excitations of a proximate Kitaev quantum spin liquid realized in Cu${}_2$IrO${}_3$
• Effective model with strong Kitaev interactions for $\alpha$-$\mathrm{RuC}{\mathrm{l}}_3$
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• Nonequilibrium Majorana Dynamics by Quenching a Magnetic Field in Kitaev Spin Liquids
• NMR Investigation on Honeycomb Iridate Ag${}_3$LiIr${}_2$O${}_6$
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• Emergent quantum Majorana metal from a chiral spin liquid
• Spin Seebeck Effect as a Probe for Majorana Fermions in Kitaev Spin Liquids
• Anderson localization of emergent quasiparticles: Spinon and vison interplay at finite temperature in a ${\mathbb{Z}}_2$ gauge theory in three dimensions
• Majorana Gap Formation in the Anisotropic Kitaev Model with Ordered Flux Configuration
• Real-time control of non-Abelian anyons in Kitaev spin liquid under energy dissipation
• Schwinger boson theory for $S=1$ Kitaev quantum spin liquids
• Static and Dynamical Spin Correlations in the Kitaev Model at Finite Temperatures via Green's Function Equation of Motion
• Emergent Kitaev materials in synthetic Fermi-Hubbard bilayers