Determine whether antiferromagnetic alignment suppresses interlayer flat-band coupling

Determine whether opposite spin alignment between adjacent kagome layers in bulk antiferromagnetic FeSn reduces the effective coupling between the Fe d_z^2-derived states sufficiently to make the strong interlayer Fe–Fe hopping required for the A-lift flat band inaccessible.

Background

The paper identifies the occupied A-lift flat-band manifold as an interlayer-dependent state dominated by Fe d_z2 orbitals. Its double-layer tight-binding analysis finds that strong interlayer Fe–Fe hopping is the common condition for producing the A-lift, while layer-dependent onsite shifts in an AFM-like configuration reduce the characteristic energy lift. However, the model treats hopping amplitudes as independent parameters and does not microscopically constrain them according to the spin alignment of the magnetic layers. The authors therefore leave unresolved whether the experimentally relevant opposite-spin stacking in bulk AFM FeSn physically weakens the d_z2-derived interlayer coupling enough to prevent the strong-coupling regime required for the A-lift.

References

From this orbital perspective, we hypothesize that the opposite spin alignment of adjacent kagome layers in bulk AFM FeSn reduces the effective coupling between these $d_{z2}$-derived states, making the strong-$|\alpha|$ regime required for the A-lift inaccessible.

— Beyond the Kagome Layer: Interlayer Origin of the Flat Band in FeSn  (2609.28968 - Zhang et al., 24 Sep 2026) in Section II, subsection “Interlayer mechanism of the experimentally relevant flat band”