MnBi2​Te4​, the first confirmed intrinsic antiferromagnetic topological
insulator, have attracted more and more attention in recent years. Here we
investigate the energy correction and lifetime of magnons in MnBi2​Te4​
caused by magnon-magnon interaction. Firstly, a first-principles calculation
was performed to get the parameters of the magnetic Hamiltonian of
MnBi2​Te4​. Then the perturbation method of many-body Green's function is
applied and the 1st-order self-energy [Σ(1)(k)] and 2nd-order
self-energy [Σ(2)(k,εk​)] of magnon are
obtained. Numerical computation shows that the correction from both
Σ(1)(k) and Σ(2)(k,εk​) are
strongly dependent on momentum and temperature, the energy renormalization near
Brillouin zone (BZ) boundary is obviously stronger than that near BZ centre. We
also find that some dip structures occur in renormalized magnon spectrum near
K and M points, and these dip structures should be attributed to
Σ(2)(k,εk​).Comment: 7 pages, 7 figure