Many-particle effects in adsorbed magnetic atoms with easy-axis anisotropy: the case of Fe on CuN/Cu(100) surface

摘要

We study the effects of the exchange interaction between an adsorbed magneticatom with easy-axis magnetic anisotropy and the conduction-band electrons fromthe substrate. We model the system using an anisotropic Kondo model and wecompute the impurity spectral function which is related to the differentialconductance (dI/dV) spectra measured using a scanning tunneling microscope. Tomake contact with the known experimental results for iron atoms on theCuN/Cu(100) surface [Hirjibehedin et al., Science {\bf 317}, 1199 (2007)], wecalculated the spectral functions in the presence of an external magnetic fieldof varying strength applied along all three spatial directions. It is possibleto establish an upper bound on the coupling constant J: in the range of themagnetic fields for which the experimental results are currently known (up to7T), the low-energy features in the calculated spectra agree well with themeasured dI/dV spectra if the exchange coupling constant J is at most half aslarge as that for cobalt atoms on the same surface. We show that for evenhigher magnetic field (between 8 and 9T) applied along the ``hollowdirection'', the impurity energy states cross, giving rise to a Kondo effectwhich takes the form of a zero-bias resonance. The paper introduces an approachfor calculating the expectation values of global spin operators and allcomponents of the impurity magnetic susceptibility tensor in numericalrenormalization group (NRG) calculations with no spin symmetry. An appendixcontains a density-functional-theory (DFT) study of the Cu and Fe adsorbates onCuN/Cu(100) surface: we compare magnetic moments, as well as orbital energies,occupancies, centers, and spreads by calculating the maximally localizedWannier orbitals of the adsorbates.