Quantized electronic fine structure with large anisotropy in ferromagnetic Fe films

We report on the spectroscopic observation of a quantized electronic fine structure near the Fermi energy in thin Fe films grown on W(110). The quantum well states are detected down to binding energies of $\ensuremath{\sim}$10 meV by angle-resolved photoelectron spectroscopy. The band dispersion of these states is found to feature a pronounced anisotropy within the surface plane: It is free-electron-like along the $\overline{\ensuremath{\Gamma}H}$ direction while it becomes heavy along $\overline{\ensuremath{\Gamma}N}$. Density functional theory calculations identify the observed states to have both majority and minority spin character and indicate that the large anisotropy can be dependent on the number of Fe layers and coupling to the substrate.