Unusual Thermal Hall Effect in a Kitaev Spin Liquid Candidate α−RuCl3

Abstract

The Kitaev quantum spin liquid displays the fractionalization of quantum spins into Majorana fermions. The emergent Majorana edge current is predicted to manifest itself in the form of a finite thermal Hall effect, a feature commonly discussed in topological superconductors. Here we report on thermal Hall conductivity κ_{xy} measurements in α-RuCl_{3}, a candidate Kitaev magnet with the two-dimensional honeycomb lattice. In a spin-liquid (Kitaev paramagnetic) state below the temperature characterized by the Kitaev interaction J_{K}/k_{B}∼80 K, positive κ_{xy} develops gradually upon cooling, demonstrating the presence of highly unusual itinerant excitations. Although the zero-temperature property is masked by the magnetic ordering at T_{N}=7 K, the sign, magnitude, and T dependence of κ_{xy}/T at intermediate temperatures follows the predicted trend of the itinerant Majorana excitations.

Giant thermal Hall conductivity in the pseudogap phase of cuprate superconductors

“…is very weak, we attribute this κ xy signal to exotic neutral excitations, presumably with spin chirality 7 . The thermal Hall conductivity in the pseudogap phase of cuprates is reminiscent of that found in insulators with spin-liquid states 8,9,10 . In the Mott insulator La 2 CuO 4 , it attains the highest known magnitude of any insulator 11 .…”

Oriented propagation of magnetization due to chiral edge modes in Kitaev-type models

“…Detecting chiral edge modes in topological materials has been a central issue in experiments as well. Actually, Kitaev-type magnets [11][12][13] in the external magnetic field are most likely candidates whose ground state is a chiral spin liquid 14,15 . Therefore, a much deeper theoretical understanding of the related phenomena is required.…”

“…(14) (red solid lines), together with the edge-mode dispersion given in Eq. (35) (a blue dashed line), showing quite good agreement with each other.…”

Topological thermal Hall effect for topological excitations in spin liquid: Emergent Lorentz force on the spinons

“…In the QSL regime, the deconfined spinons transport heat in the same way that the physical electrons carry charge in an electrical conductor. However, a major difficulty is that other excitations, most notably phonons, may get involved in the longitudinal thermal conductivity [6][7][8][9][10][11][12][13][14]. The quantitative contribution of spin excitations may be difficult to be extracted from the total longitudinal thermal conductivity due to the spin-phonon interaction, which is suggested to be present in many materials, especially in the ones with strong spin-orbit coupling.…”