We study the spin transport through the quantum spin liquid (QSL) by investigating the real-time and realspace dynamics of the Kitaev spin system with a zigzag structure in terms of the time-dependent Majorana mean-field theory. After the magnetic field pulse is introduced to one of the edges, the spin moments are excited in the opposite edge region although no spin moments are induced in the Kitaev QSL region. This unusual spin transport originates from the fact that the S = 1/2 spins are fractionalized into the itinerant and localized Majorana fermions in the Kitaev system. Although both Majorana fermions are excited by the magnetic pulse, only the itinerant Majorana fermions flow through the bulk regime without the spin excitation, resulting in the spin transport in the Kitaev system. We also demonstrate that this phenomenon can be observed even in the system with the Heisenberg interactions using the exact diagonalization.

We investigate the real-time spin response of the S = 1 Kitaev model upon stimuli of a pulsed magnetic field in the one of the edges using the exact diagonalization method. It is found that the pulsed magnetic field has no effect on the appearance of the spin moments in the quantum spin liquid region, but induces the spin oscillations in the other edge region with a small magnetic field. This is understood by the existence of the itinerant quasiparticles, which carries the spin excitations without the spin polarization in the quantum spin liquid state. This suggests that the spin fractionalizations occur in the S = 1 Kitaev model as well as the exactly solvable S = 1/2 Kitaev one and the fractionalized quasiparticles play an essential role in the spin transport.The Kitaev model has attracted much interest since the proposal of the quantum spin model by A. Kitaev 1) and suggestion of its implementation in real materials. 2) This model is composed of direction-dependent Ising exchange interactions on a honeycomb lattice, which is exactly solvable and its ground state is a quantum spin liquid (QSL) with short-range spin correlations. In this model, quantum spins are fractionalized into the localized and itinerant Majorana fermions due to the quantum many-body effect. 1, 3-5) The Majorana fermions have been observed recently as a half-quantized plateau in the thermal quantum Hall experiments in the candidate material α-RuCl 3 . 6-10) Furthermore, it is theoretically clarified that distinct energy scales ascribed to the fractionalization appear in the thermodynamic properties such as a double-peak structure in the specific heat, 11,12) which stimulates further theoretical and experimental investigations on the spin fractionalization. [13][14][15][16][17][18] Recently, the generalization of the Kitaev model with arbitrary spins 19) has been studied, [20][21][22][23][24][25][26][27][28][29] where similar double peaks in the specific heat have been reported. 21) Therefore, the spin fractionalizations are naively expected even in the spin-S Kitaev model although it is no longer solvable.In our previous manuscipt, 30) we have studied the real-time dynamics of the S = 1/2 Kitaev model by means of the Majorana mean-field theory. It has been found that, even in the Kitaev QSL with extremely short-ranged spin correlations, the spin excitation propagates in the bulk without spin polarization. This suggests that the spin transport is not caused by the change of local magnetization, but is mediated by the itinerant Majorana fermions. Therefore, the real-time simulation for the spin transport is one of the promising approaches to examine the existence of the itinerant quasiparticles in the spin-S Kitaev model.In this paper, we investigate the real-time dynamics of the S = 1 Kitaev model on the honeycomb lattice with two edges by means of the exact diagonalization method. We demonstrate that after the pulsed magnetic field is applied to one of the edges, the oscillation of spin moments does not appear in the bulk, but is induced in...

We study low-energy properties of spin-S Kitaev models in an anisotropic limit. The effective form of a local conserved quantity is derived in the low-energy subspace. We find this is the same as that of S = 1/2 case for the half-integer spins but shows a different form for the integer spins. Applying the perturbation theory to the anisotropic Kitaev model, we obtain the effective Hamiltonian. In the integer spin case, the effective model is equivalent to a free spin model under an uniform magnetic field, where quantum fluctuations are quenched. On the other hand, in the half-integer case, the system is described by the toric code Hamiltonian, where quantum fluctuations play a crucial role in the ground state. The boundary effect in the anisotropic Kitaev system is also discussed.

We investigate magnetic properties in the S = 1 Kitaev model in the anisotropic limit. Performing the fourth-order perturbation expansion with respect to the x-bonds, y-bonds, and magnetic field, we derive the effective Hamiltonian, where the low-energy physics should be described by the free spins with an effective magnetic field. Making use of the exact diagonalization method for small clusters, we discuss ground-state properties in the system complementary.