Junki Yoshitake

Thermal Transport in the Kitaev Model

In conventional insulating magnets, heat is carried by magnons and phonons. In contrast, when the magnets harbor a quantum spin liquid state, emergent quasiparticles from the fractionalization of quantum spins can carry heat. Here, we investigate unconventional thermal transport yielded by such exotic carriers, in both longitudinal and transverse components, for the Kitaev model, whose ground state is exactly shown to be a quantum spin liquid with fractional excitations described as itinerant Majorana fermions and localized Z_{2} fluxes. We find that the longitudinal thermal conductivity exhibits a single peak at a high temperature, while the nonzero frequency component has a peak at a low temperature, reflecting the spin fractionalization. On the other hand, we show that the transverse thermal conductivity is induced by the magnetic field in a wide temperature range up to the energy scale of the bare exchange coupling; while increasing temperature, the transverse response divided by temperature decreases from the quantized value expected for the topologically nontrivial ground state and shows nonmonotonic temperature dependence. These characteristic behaviors provide experimentally accessible evidence of fractional excitations in the proximity to the Kitaev quantum spin liquid.

Charge order in a two-dimensional Kondo lattice model.

The possibility of charge order is theoretically examined for the Kondo lattice model in two dimensions, which does not include bare repulsive interactions. Using two complementary numerical methods, we find that charge order appears at quarter filling in an intermediate Kondo coupling region. The charge ordered ground state is an insulator exhibiting an antiferromagnetic order at charge-poor sites, while the paramagnetic charge-ordered state at finite temperatures is metallic with pseudogap behavior. We confirm that the stability of charge order is closely related with the local Kondo-singlet formation at charge-rich sites. Our results settle the controversy on charge order in the Kondo lattice model in realistic spatial dimensions.

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

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 (

Temperature evolution of spin dynamics in two- and three-dimensional Kitaev models: Influence of fluctuating Z2 flux

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Trimer Formation and Metal–Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice

) 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

Majorana fermions in the Kitaev quantum spin system α-RuCl3

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Fractional Spin Fluctuations as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model

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

Incarnation of Majorana Fermions in Kitaev Quantum Spin Lattice

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The realization of Majorana fermions in Kitaev Quantum Spin Lattice

scales. Extending the previous study for the isotropic coupling case [J. Yoshitake, J. Nasu, and Y. Motome, Phys. Rev. Lett.

Liquid-Liquid Transition in Kitaev Magnets Driven by Spin Fractionalization

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