Physcial properties of high-quality single crystals of the Kitaev spin liquid candidate α-RuCl3 grown by the sublimation method

Kitaev spin liquid is an attractive state which exhibits exotic excitations of fractionalized Majorana fermions. As a promising candidate for the Kitaev spin liquid, α-RuCl₃ has been actively studied. In this material, the half-integer quantization of thermal Hall conductivity has been observed and interpreted as a signature of edge current state of Majorana fermions. Also, specific heat measurements have reported peculiar magnetic field angle dependence that reflects the Majorana gap. These results are considered to be strong evidence for the realization of the Kitaev spin liquid in α-RuCl₃.

However, it has been pointed out that the results of the thermal Hall effect depend on the growth method or crystal quality of samples. Especially, the quantization of thermal Hall conductivity tends to be observed in samples with higher quality and longer mean free paths. Therefore, it is important to synthesize high-quality samples of α-RuCl₃ with various methods and examine the influence of these sample dependences on the Kitaev spin liquid state. 

Here, we synthesized high-quality samples of α-RuCl₃ by the sublimation method. The quality of samples has been confirmed with the larger and sharper specific heat anomaly at antiferromagnetic transition and the largest longitudinal thermal conductivity in the antiferromagnetic phase reported so far. We also performed specific heat measurements in magnetic field and examined Kitaev spin liquid state. We will discuss these results and compare with the reported data in samples synthesized by other methods.