We have investigated the sample dependence of the half-integer thermal Hall effect in $\alpha \text{−}{\mathrm{RuCl}}_3$ under a magnetic field tilted ${45}^{\circ }$ from the $c$ axis to the $a$ axis. We find that the sample with the largest longitudinal thermal conductivity ${\kappa }_{xx}$ shows the half-integer quantized thermal Hall effect expected in the Kitaev model. On the other hand, the quantized thermal Hall effect was not observed in the samples with smaller ${\kappa }_{xx}$. We suggest that suppressing the magnetic scattering effects on the phonon thermal conduction, which broaden the field-induced gap protecting the chiral edge current of the Majorana fermions, is important to observe the quantized thermal Hall effect.

• Received 27 April 2020
• Revised 13 November 2020
• Accepted 23 November 2020

DOI:https://doi.org/10.1103/PhysRevB.102.220404