Anomalous Zeeman shift of defect-bound states in epitaxial FeSn films

We synthesize high-quality FeSn thin films on SrTiO 3 (111) substrates by molecular beam epitaxy. Using in situ low-temperature scanning tunneling microscopy/spectroscopy, we observe honeycomb lattice on the Sn-terminated films and close-packed lattice for the Fe 3 Sn termination. In addition, we also directly visualize single Sn vacancy in the Fe 3 Sn layer and di-vacancy in the Sn layer, as well as their response to applied magnetic fields. The bound states induced by these defects exhibit anomalous Zeeman shifts in out-of-plane magnetic fields, where the energy of the bound states shifts linearly towards higher energy independent of the direction of the magnetic field. A two-fold oscillatory response to in-plane magnetic fields is also observed. These findings provide critical insights into under-standing magnetism in Kagome magnetic materials.