Valence fluctuations and Kondo resonance in Co adatom on Cu₂N/Cu(100) surface:DFT + ED study

We report density functional theory plus exact diagonalization of the multi-orbital Anderson impurity model calculations including the spin-orbit coupling for the Co adatom on the top of Cu₂N/Cu(001) surface. It is found that experimentally observed zero-bias peak in differential conductance can occur for quasi-degenerate many-body solution representing a mixed valence state of the Co adatom with the non-integer d manifold occupation of 7.4. Estimated 5 meV inelastic step energy is in a quantitative agreement with the experimental scanning tunnelling spectroscopy value of 6 meV. We find the non-zero spin and orbital magnetic moments in the applied magnetic field, in a reasonable agreement with the x-ray magnetic circular dichroism data. The presence of large orbital magnetic moment was not considered in previous spin-only theoretical interpretations, and can unravel complexity of the physics behind the experimental spectra for Co and other adatoms on Cu₂N/Cu(001) surface.