Dirac Semimetallicity Enabled by Stripe Antiferromagnetism in Monolayer FeSe

Monolayer FeSe is a central platform for iron‐based superconductivity, yet the electronic phases emerging from its competing magnetic orders remain elusive. Here we identify a Dirac semimetal state in monolayer FeSe induced by stripe antiferromagnetism, which hosts symmetry‐protected Dirac nodes near the Fermi level. We show that breaking a single mirror symmetry enables an odd inter‐orbital coupling between opposite‐parity Fe states, enforcing robust Dirac crossings with a nontrivial Wilson‐loop topology and boundary‐dependent edge modes. We further predict a strong orbital diamagnetic susceptibility as a direct experimental fingerprint of this Dirac phase. Our work establishes FeSe as a magnetically tunable route to topological quasiparticles in iron‐based two‐dimensional quantum materials.