The Kitaev quantum spin liquid (QSL) on the two-dimensional honeycomb lattice epitomizes an entangled topological state, where the spins fractionalize into Majorana fermions. This state has aroused tremendous interest because it harbors non-Abelian anyon excitations. The half-integer quantized thermal Hall (HIQTH) conductance observed in α-RuCl3 is a key signature of these excitations. However, the fate of this topologically nontrivial state at intense fields remains largely elusive. Here, we report the thermal conductivity κ and specific heat C of α-RuCl3 with in-plane magnetic fields H. For the field direction perpendicular to the Ru-Ru bond, where the HIQTH effect is observed, we find a discontinuous jump in κ(H) and a peak anomaly in C(H) at μ0H∗≈11\,T, evidencing a weak first-order phase transition. Remarkably, the HIQTH effect vanishes close to H∗. Furthermore, we find that the spin-fractionalization feature is retained well above H∗. These imply the emergence of the phase transition that separates two QSL phases with distinct topological properties.
@article{arxiv.2203.00275,
title = {Evidence for the first-order topological phase transition in a Kitaev spin liquid candidate $\alpha$-RuCl$ _3$},
author = {S. Suetsugu and Y. Ukai and M. Shimomura and M. Kamimura and T. Asaba and Y. Kasahara and N. Kurita and H. Tanaka and T. Shibauchi and J. Nasu and Y. Motome and Y. Matsuda},
journal= {arXiv preprint arXiv:2203.00275},
year = {2022}
}