Field-angle dependence of thermal Hall conductivity in a magnetically ordered Kitaev-Heisenberg system

Abstract

We study magnetic excitations and thermal Hall effect on the Kitaev-Heisenberg model under magnetic fields. By employing the spin-wave theory for the magnetic orders realized in this model, we examine the topological nature of the spin-wave dispersions and calculate the thermal Hall conductivity. The comprehensive investigations on the field-angle dependence clarify that the thermal Hall conductivity is sensitive to the spin ordered pattern and excitation spectra of magnons; this quantity is enhanced by the noncoplanar spin configurations and small magnon gap in the excitation spectrum. On the other hand, we also find a common feature in the field-angle dependence of the thermal Hall conductivity. It vanishes when the magnetic field is on the planes spanned by the spin axes. We reveal that the behavior is intrinsic to the Kitaev-Heisenberg model in an applied field and demonstrate that the introduction of the off-diagonal spin interaction causes the disappearance of the feature in the thermal Hall conductivity.

Majorana-fermion origin of the planar thermal Hall effect in the Kitaev magnet α-RuCl 3

“…1C ). Thus, the topological transition between different Chern numbers, which can be induced by field-angle rotations, accompanies a complete closure of low-energy excitation gap only for the Majorana fermion case ( 27 , 29 ).…”

Field-angle dependence of thermal transport in Kitaev-Γ model

“…This property is clearly seen in Fig. 1(c), and it is maintained even in the presence of the Heisenberg interaction but is not for the Γ one [14]. The sign of κ ab depends on the direction of the applied magnetic field.…”

“…In Eq. ( 2), M k is a 2M × 2M Hermitian matrix, which is obtained by the Holstein-Primakoff transformation [14]. By diagonalizing M k using the Bogoliubov transformation with the transform matrix J k , we evaluate the magnon energy ε n,k for the nth branch.…”

“…With increasing temperature, κ ab /T is enhanced, but there are several nodal points where it remains zero for the temperature evolution. In particular, for the magnetic field parallel to the b axis, κ ab vanishes because of the symmetry [14].…”

Scattering phenomena for spin transport in Kitaev spin liquid

“…The signatures of these fractional quasiparticles manifest themselves in the measurements for the specific heat and excitation spectra, such as neutron and Raman scatterings in the candidate materials [53][54][55][56][57][58][59][60][61][62][63]. Interestingly, applying weak magnetic fields causes the topologically nontrivial band structure of the Majorana fermions [64][65][66][67][68][69][70][71][72][73][74][75][76][77]. Moreover, as a counterpart of a Majorana edge mode, each flux excitation traps a Majorana zero mode, which behaves as a non-Abelian anyon [24].…”