Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na${}_2$Co${}_2$TeO${}_6$

Abstract

The recent report of a half-quantized thermal Hall effect in the Kitaev material $\alpha$-RuCl${}_3$ has sparked a strong debate on whether it is generated by Majorana fermion edge currents or whether other more conventional mechanisms involving magnons or phonons are at its origin. A more direct evidence for Majorana fermions which could be expected to arise from a contribution to the longitudinal heat conductivity ${\kappa }_{xx}$ at $T\to 0$ is elusive due to a very complex magnetic field dependence of ${\kappa }_{xx}$. Here, we report very low temperature (below 1~K) thermal conductivity ($\kappa$) of another candidate Kitaev material, Na${}_2$Co${}_2$TeO${}_6$. The application of a magnetic field along different principal axes of the crystal reveals a strong directional-dependent magnetic-field ($\mathbf{B}$) impact on $\kappa$. We show that no evidence for mobile quasiparticles except phonons can be concluded at any field from 0~T to the field polarized state. In particular, severely scattered phonon transport is observed across the $B-T$ phase diagram, which is attributed to prominent magnetic fluctuations. Cascades of phase transitions are uncovered for all $\mathbf{B}$ directions by probing the strength of magnetic fluctuations via a precise record of $\kappa$($B$). Our results thus rule out recent proposals for itinerant magnetic excitations in Na${}_2$Co${}_2$TeO${}_6$, and emphasise the importance of discriminating true spin liquid transport properties from scattered phonons in candidate materials.

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Cited by in corpus (15)

• Ferrimagnetism from triple-q order in Na${}_2$Co${}_2$TeO${}_6$
• Charge-Neutral Electronic Excitations in Quantum Insulators
• Signatures of a Quantum Critical Endpoint in the Kitaev Candidate Na${}_2$Co${}_2$TeO${}_6$
• On the multi-$\mathbf{q}$ characteristics of magnetic ground states of honeycomb cobalt oxides
• Spin waves in Na${}_2$Co${}_2$TeO${}_6$ studied by high-frequency/high-field ESR: Successes and failures of the triple-$\mathbf{q}$ model
• Ferrimagnetism from quantum fluctuations in Kitaev materials
• Competing Interactions and the Effects of Uniaxial Out-of-plane Perturbations in the Honeycomb Antiferromagnet Na${}_2$Co${}_2$TeO${}_6$
• Phonon Thermal Hall Effect: The Roles of Disorder, Annealing, and Metallic Contacts
• Phenomenological Ginzburg-Landau theory for triple-Q magnetic orders on a hexagonal lattice
• Spin-phonon coupling and thermal Hall effect in the Kitaev model
• Using magnetic dynamics to measure the spin gap in a candidate Kitaev material
• Itinerant and topological excitations in a honeycomb spiral spin liquid candidate
• Scaling behavior and giant field-enhancement of the thermal conductivity in the honeycomb antiferromagnet BaCo2(AsO4)2
• Real-space chirality from crystalline topological defects in the Kitaev spin liquid
• Direct probe of magnetic field effects on phonons by ultrasound propagation in a quasi-two-dimensional honeycomb magnet Na${}_2$Co${}_2$TeO${}_6$