Thermal transport of fractionalized antiferromagnetic and field-induced states in the Kitaev material <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Na</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Co</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>TeO</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math>
Shuangkui Guang, Na Li, Rui Leonard Luo, Qing Huang, Yiyan Wang, Xiaoyue Yue, Ke Xia, Qiuju Li, Xia Zhao, Gang Chen, Haidong Zhou, X. F. Sun
Abstract
We report an in-plane thermal transport study of the honeycomb Kitaev material ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}{\mathrm{TeO}}_{6}$ at sub-Kelvin temperatures. In zero magnetic field, the $\ensuremath{\kappa}(T)$ displays a rather weak $T$ dependence but has a nonzero residual term ${\ensuremath{\kappa}}_{0}/T$, indicating strong phonon scattering by magnetic excitation and the possibility of itinerant spinonlike excitations coexisting with an antiferromagnetic order below 27 K. We propose the zero-field ground state is a fractionalized antiferromagnetic (AF*) state with both magnetic order and fractionalized excitations. With both the heat current and magnetic field along the $a*$ (Co-Co bond) direction, the ${\ensuremath{\kappa}}_{a*}(B)$ exhibits two sharp minima at 7.5 and 10 T, which confirms the phase boundaries of the reported field-induced intermediate state. No such intermediate phase was found in the ${\ensuremath{\kappa}}_{a}(B)$ for the current and field along the $a$ (zigzag chain) direction. Finally, ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}{\mathrm{TeO}}_{6}$ displays a strongly anisotropic magneto-thermal conductivity since the in-plane (out-of-plane) field strongly enhances (suppresses) ${\ensuremath{\kappa}}_{a*}$ and ${\ensuremath{\kappa}}_{a}$.