Thermal signatures of strong magnon-phonon interactions in the canted anti-ferromagnetic phase of MnBi₂Te₄

Stacked van de Waals septuple layers in MnBi₂Te₄ displays an intriguing combination of spin-orbit coupling induced band inversion in Bi₂Te₃ layers and magnetic moments provided by MnTe layers. Below the Neel temperature T_N=25K, MnBi₂Te₄ becomes an antiferromagnetic (AFM) topological insulator. In an increasing magnetic field applied perpendicular to the layers, the magnetic ordering undergoes a spin-flop transition followed by a canted-antiferromagnetic (CAFM) ordering and finally into a ferromagnetic (FM) ordering where the interlayer magnetic exchange coupling induces a magnetic Weyl semimetal phase [1]. Here, we report field dependence of thermal conductivity k in the in-plane direction under an applied magnetic field in the cross-plane direction in MnBi₂Te₄ from 2K to 30K. k shows a drop in the CAFM phase which we attributed to strong magnon-phonon scattering. We also report thermal Hall data measured in the same configuration and compare it with the electrical Hall data.

[1] Lei & al. PNAS 117 (44) 27224-27230 (2020)