Separation of electron and magnetic order dynamics in magnetic topological insulator MnBi₂Te₄

MnBi₂Te₄ is one of the few known intrinsic magnetic topological insulators. Various exotic properties have been demonstrated, including the axion insulating state and the quantum anomalous Hall effect. Despite a plethora of equilibrium spectroscopic studies, a number of mysteries remain unresolved. In particular, the interaction between the topological electronic band and magnetism in this material, manifested by a broken time-reversal symmetry gap, is under intense debate. Meanwhile, time-resolved spectroscopies provide a possible route to disentangle electronic, magnetic, and lattice degrees of freedom in the time domain, which may shed light on the fundamental mysteries in MnBi₂Te₄. To understand the electron-phonon and electron-magnon coupling in MnBi₂Te₄, we have performed time- and angle-resolved photoemission spectroscopy (trARPES) experiments using 1.5 eV infrared pump and 6 eV ultraviolet probe. At very low pumping fluences, the electronic ensemble reaches transient temperatures that are orders of magnitude higher than the Néel temperature, yet signatures of magnetism are barely changed. This spectroscopic evidence indicates the separation of the dynamics of the electrons and magnetic order in this material.