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Kitaev quantum spin liquid (QSL) displays the fractionalization of quantum spins into Majorana fermions. In magnetic fields, the emergence of Majorana edge current leads to a half-integer quantized thermal Hall conductance, which has recently been reported for the two-dimensional honeycomb material α-RuCl₃ [1]. We find that the thermal Hall plateau appears even for a magnetic field with no out-of-plane components, which is in stark contrast to the conventional electronic Hall effect that requires a perpendicular magnetic field. Field-angular variation of the topological Chern number determined by the sign of the quantized thermal Hall conductance is consistent with that predicted for the pure Kitaev QSL. These results provide evidence that the Kitaev interaction is of prime importance for realizing the non-Abelian topological order in α-RuCl₃ [2].

[1] Y. Kasahara et al., Nature 559, 227-231 (2018).
[2] T. Yokoi et al., arXiv:2001.01899.