Anisotropic in-plane heat transport of Kitaev magnet Na$_2$Co$_2$TeO$_6$

TL;DR

This study investigates low-temperature in-plane heat transport in the Kitaev magnet Na$_2$Co$_2$TeO$_6$, revealing magnetic transitions and potential changes in magnon topology under high magnetic fields.

Contribution

It provides new insights into magnetic transitions and magnon behavior in Na$_2$Co$_2$TeO$_6$ through detailed thermal conductivity measurements under magnetic fields.

Findings

An anomaly at 10.25--10.5 T indicating a magnetic transition.

Weak low-field signals and sign change in thermal Hall conductivity at high fields.

Constraints on high-field magnetic phases and theoretical models.

Abstract

We report a study on low-temperature heat transport of Kitaev magnet Na$_2$Co$_2$TeO$_6$, with the heat current and magnetic fields along the honeycomb spin layer (the $ab$ plane). The zero-field thermal conductivity of $\kappa^a_{xx}$ and $\kappa^{a*}_{xx}$ display similar temperature dependence and small difference in their magnitudes; whereas, their magnetic field (parallel to the heat current) dependence are quite different and are related to the field-induced magnetic transitions. The $\kappa^a_{xx}(B)$ data for $B \parallel a$ at very low temperatures have an anomaly at 10.25--10.5 T, which reveals an unexplored magnetic transition. The planar thermal Hall conductivity $\kappa^a_{xy}$ and $\kappa^{a*}_{xy}$ show very weak signals at low fields and rather large values with sign change at high fields. This may point to a possible magnetic structure transition or the change of the magnon band topology that induces a radical change of magnon Berry curvature distribution before entering the spin polarized state. These results put clear constraints on the high-field phase and the theoretical models for Na$_2$Co$_2$TeO$_6$.