Transport detection of chiral magnons in the Weyl magnet MnSb₂Te₄

Magnons — the bosonic quanta of spin wave excitations — are the carriers of spin currents in both ferromagnetic (FM) and antiferromagnetic (AFM) materials. In contrast to ferromagnets, AFM magnons can possess distinctive dual chirality: the right-handed and left-handed precession modes that thus far have been mainly accessed by polarized photonic probes. Here we report the first detection of chiral magnon eigenmodes in charge transport in the van der Waals layered Weyl semimetal MnSb₂Te₄ (MST). Chirality switching is realized in AFM MST at the field-driven spin-reorientation transitions — a 1^st order spin-flop transition at H₁ (for H||c) and spin-flip at H₂ (for H||ab) when Mn moments align with the applied magnetic field H; both the spin and orbital moments of magnons contribute to their electrical activity. These characteristic AFM fields, straightforwardly obtained from magnetoresistance R_xx(H), are tunable by carrier density, which we control using hydrogen intake in the p-type MST [1]. At low temperatures, both AFM and FM states exhibit gapped magnon transport ΔR_xx = ATⁿexp(-E_m/T), where n = ½ for AFM and n = 1 for FM, reflecting their different Weyl bandstructures. Chirality switching in the AFM MST is recorded when the magnon gap energy E_m → 0 in a discontinuous manner [2]. Such switching is absent in the FM MST. Notably, spin-reorientation in MST proceeds via proliferation of domain walls (DWs) that can interact with chiral magnons and contribute to R_xx(T, H). We discuss a scenario in which emergent axial gauge fields, by generating localized charges at the DWs, couple to Weyl quasiholes inhabiting MST to reflect magnon chirality in their current-driven transport.



[1] A. N. Tamanna, A. Lakra, X. Ding, E. Buzi, K. Park, K. Sobczak, H. Deng, G. Sharma, S. Tewari, and L. Krusin-Elbaum, Nature Comms. 15, 9830 (2024).

[2] A. Lakra, E. Buzi, J. Moon, A.N. Tamanna, K. Sobczak, K. Park, S. Takei, and L. Krusin-Elbaum., manuscript in preparation (2025).