Spin excitations in the intrinsic magnetic topological insulator MnBi2Te4

Recently, the first intrinsic magnetic topological insulator has been realized in MnBi2Te4. MnBi2Te4 has a tetradymite-type structure with seven-atom layers coupled by the van der Waals interaction along the z direction (e.g., Te1-Bi1-Te2-Mn-Te3-Bi2-Te4), Its magnetic ground state is A-type antiferromagnetic phase with the out-of-plane easy axis and Neel temperature TN=25 K. Here, time-reversal symmetry is broken, but the combination of time reversal and a half-lattice translation connecting nearest spin-up and -down Mn atomic layers is not broken, giving the possible topologically nontrivial phenomena, such as topological axion state, QAH effect, two-dimensional ferromagnetism, etc. To understand the magnetic interactions and thus the interplay between magnetism and topological states in MnBi2Te4, here we propose to do inelastic neutron scattering experiment at MAPS.