Revealing Termination-Selective Modifications in the Topological Surface States of Mn(Sb_xBi_1-x)₄Te₇ via Time-Reversal Dichroism in ARPES

The layered material MnBi₄Te₇ provides a platform to study the interplay between magnetism and topology. Partial substitution of Bi by Sb in Mn(Sb_0.15Bi_0.85)₄Te₇ drives the system from an antiferromagnetic to a ferromagnetic ground state while preserving the crystal structure. Here, we present time-reversal circular dichroism measurements using a laser-based μ-ARPES system, which can selectively probe the vectorial components of the orbital angular momentum in the two distinct surface terminations. In combination with bandstructure calculations, we track the spin–orbit texture of the surface states across the entire Brillouin zone and as a function of Sb substitution. Our measurements reveal termination-dependent chemical potential shifts and changes in the hybridization between surface and bulk bands. We discuss our results in the context of preferential Sb occupation sites and layer-dependent magnetic structures.