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Accepted · first revision · record

Title: What carries the thermal Hall signal in $\alpha$-RuCl3?
Plain: Heat flowing through $\alpha$-RuCl3 in a magnetic field is deflected sideways, an effect called the thermal Hall effect. It is unclear whether the sideways heat is carried by Majorana fermions of a spin liquid, by magnons (spin waves) or by phonons (lattice vibrations).
Precise: In alpha-RuCl3 with field H of 60 to 120 kOe in the honeycomb plane and T of 2 to 20 K, identify the carriers responsible for $\kappa_{xy}(T,H)$: chiral Majorana edge modes, topological magnons, or phonons with field-induced Berry curvature or Hall viscosity. An answer is a microscopic model that reproduces $\kappa_{xy}(T,H)$ and its dependence on field angle, sample quality and $\kappa_{xx}$ across published samples.
Settled by: Measurements of $\kappa_{xy}$ on many samples with characterized stacking, combined with phonon and magnon calculations from the measured spin Hamiltonian, that isolate one dominant channel.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: Phonon (Lefrancois et al., PRX 2022) and magnon (Czajka et al., Nature Materials 2023) explanations compete with the Majorana interpretation; Shragai et al. (Nature 2026) measured a phonon Hall viscosity that accounts for a substantial fraction of $\kappa_{xy}$.
Posed since: 2018