Field-induced first-order topological phase transition in a Kitaev spin liquid candidate α-RuCl₃

The honeycomb magnet α-RuCl₃ is a prime candidate for the Kitaev quantum spin liquid as revealed by the half-integer quantized thermal Hall (HIQTH) conductivity κ_xy in the field-induced paramagnetic state, indicating the emergence of non-abelian anyon. However, the fate of this topologically nontrivial state at intense fields remains largely elusive. Here, we report longitudinal thermal conductivity κ_xx in in-plane magnetic fields. Remarkably, κ_xx at very low temperatures exhibits a discontinuous jump at μ₀H* = 11 T for bond perpendicular field direction along which the HIQTH effect is observed. We find that this H* is close to the field at which the HIQTH effect vanishes, demonstrating the emergent first-order topological phase transition.