Transition signatures in the magnetothermal conductivity of α-RuCl₃

We report measurements of the thermal conductivity κ_xx in the Kitaev spin liquid candidate α-RuCl₃, performed on high-quality single crystals as a function of magnetic field B applied within the plane, for directions B || a and B || b, at temperatures down to 0.1 K.



We observe oscillations in κ_xx vs B that are characterized by four minima – located at B₁, B₂, B₃ and B₄. The first two minima, at B₁ ≈ 6 T and B₂ ≈ 7.5 T are clearly associated with the end of the antiferromagnetic phase at B_c2 ≈ 7.5 T (and its internal transition at B_c1 ≈ 6 T).



The upper two minima have been attributed to quantum oscillations associated with fermionic excitations (spinons) in a putative quantum spin liquid state, which would end at a threshold field B* ~ 12 T (for B || a) [1], above which κ_xx(B) is featureless, free of oscillations and constant with field.



In agreement with others [2], we instead attribute the upper minima at B₃ and B₄ to secondary magnetic transitions, given that we find their anisotropy (B || a vs B || b) to track the anisotropy of the transition field B*.



[1] Czajka et al., Nat. Phys. 17, 915 (2021).

[2] Bruin et al., APL Mat. 10, 090703 (2022).