Fluctuation Mechanism of Single-Ion Anisotropy of Topological Insulator MnBi${}_2$Te${}_4$

V. V. Val'kov, A. O. Zlotnikov, A. Gamov

We demonstrate that charge fluctuations induced by electron hopping, combined with spin-orbit coupling, lift the sixfold degeneracy of the orbital singlet ${}^{6}S$ of Mn ions in the…