Momentum-inversion symmetry breaking on the Fermi surface of magnetic topological insulators

Magnetic topological insulators (MnBi2Te4)(Bi2Te3)n were anticipated to exhibit magnetic energy gaps, while recent spectroscopic studies did not observe them. Thus, magnetism on the surface is under debate. In this work, we propose another symmetry criterion to probe surface magnetism. Because of both time-reversal symmetry breaking and inversion symmetry breaking, we demonstrate that the surface band structure violates momentum-inversion symmetry and leads to a threefold rather than sixfold rotational symmetry on the Fermi surface if corresponding surface states couple strongly to the surface magnetism. Such a momentum-inversion symmetry violation is significant along the Γ-K direction for surface bands on the (0001) plane, which serves as a criterion for determining the surface magnetism.