Defect-induced low-energy Majorana excitations in the Kitaev magnet α-RuCl₃

Recently, the layered honeycomb material α-RuCl₃ exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) under an in-plane magnetic field. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions. However, it has been reported that the thermal Hall conductivity shows strong sample dependence. Therefore, in order to understand the nature of the high-field state, it is crucial to elucidate the effects of disorder, which inevitably exists in real materials. Here, we artificially introduce point defects by electron irradiation and compare the low-energy excitations in the pristine and irradiated sample by high-resolution specific heat measurements under in-plane magnetic field rotation[1]. We find a slight suppression of AFM order and the field-dependent Majorana gap similar to the pristine sample in the high-field state. In addition, we observe a field-dependent additional T-linear term in C/T, which indicates that low-energy excitations with a linear density of states emerge. The C/T data show the scaling behaviors with the Majorana gap, which is consistent with recent theoretical calculations.



[1] K. Imamura et al., arXiv:2306.17380 (2023).