Phononic-magnetic dichotomy of the thermal Hall effect in the Kitaev-Heisenberg candidate material Na${}_2$Co${}_2$TeO${}_6$

Abstract

Majorana fermions as emergent excitations of the Kitaev quantum spin liquid ground state constitute a promising concept in fault tolerant quantum computation. Experimentally, the recently reported topological half-quantized thermal Hall effect in the Kitaev material $\alpha$-RuCl${}_3$ seems to confirm the Majorana nature of the material's magnetic excitations. It has been argued, however, that the thermal Hall signal in $\alpha$-RuCl${}_3$ rather stems from phonons or topological magnons than from Majorana fermions. Here we investigate the thermal Hall effect of the closely related Kitaev quantum material Na${}_2$Co${}_2$TeO${}_6$, and we show that the thermal Hall signal emerges from at least two components, phonons and magnetic excitations. This dichotomy results from our discovery that the transversal heat conductivity ${\kappa }_{xy}$ carries clear signatures of the phononic ${\kappa }_{xx}$, but changes sign upon entering the low-temperature, magnetically ordered phase. We systematically resolve the two components by considering the detailed temperature and field dependence of both ${\kappa }_{xy}$ and ${\kappa }_{xx}$. Our results demonstrate that uncovering a genuinely quantized magnetic thermal Hall effect in a Kitaev topological quantum spin liquid requires to disentangle phonon vs. magnetic contributions where the latter include potentially fractionalized excitations such as the expected Majorana fermions.

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Cited by in corpus (14)

• Kitaev Quantum Spin Liquids
• Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na${}_2$Co${}_2$TeO${}_6$
• Thermal Hall effects due to topological spin fluctuations in YMnO${}_3$
• Ferrimagnetism from triple-q order in Na${}_2$Co${}_2$TeO${}_6$
• Planar thermal Hall effect from phonons in cuprates
• Exchange striction induced thermal Hall effect in van der Waals antiferromagnet MnPS${}_3$
• Phonon thermal Hall effect in non-magnetic Y${}_2$Ti${}_2$O${}_7$
• High Chern numbers and topological flat bands in high-field polarized Kitaev magnets on the star lattice
• Successive topological phase transitions in two distinct spin-flop phases on the honeycomb lattice
• Large Thermal Hall Effect in MnPS${}_3$
• Ferrimagnetism from quantum fluctuations in Kitaev materials
• Using magnetic dynamics to measure the spin gap in a candidate Kitaev material
• Susceptibility anisotropy and absence of ferroelectric order in the Kitaev spin liquid candidate Na${}_2$Co${}_2$TeO${}_6$
• Direct probe of magnetic field effects on phonons by ultrasound propagation in a quasi-two-dimensional honeycomb magnet Na${}_2$Co${}_2$TeO${}_6$