Quantized and unquantized thermal Hall conductance of the Kitaev spin liquid candidate α-RuCl3

Despite extensive investigations, a topological state that hosts Majorana edge modes in the magnetic field-induced quantum disordered state of the Kitaev candidate material α-RuCl3 has been hotly debated. To gain more insight into this issue, we measured the thermal Hall conductivity κxy of various samples grown by the Bridgman method. The results show that the half-integer quantum thermal Hall effect is intimately related to the magnitude of longitudinal thermal conductivity and the Néel temperature at zero field, both of which are sample dependent. Samples exhibiting the half-integer quantum thermal Hall effect have larger zero-field thermal conductivity values than a threshold value, implying that a long mean free path of heat carriers is an important prerequisite. In addition, we find that samples with a higher Néel temperature exhibit a higher magnetic field at which quantization starts to occur. These results indicate that the quantization phenomenon is significantly affected by the impurity scatterings and the non-Kitaev interactions.