Electronic properties of transition metal atoms onCu2N/Cu(100)

Abstract

We study the nature of spin excitations of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co, and Ni) deposited on a Cu 2 N/Cu(100) surface using both spin-polarized density functional theory (DFT) and exact diagonalization of an Anderson model derived from DFT. We use DFT to compare the structural, electronic, and magnetic properties of different transition metal adatoms on the surface. We find that the average occupation of the transition metal d shell, main contributor to the magnetic moment, is not quantized, in contrast with the quantized spin in the model Hamiltonians that successfully describe spin excitations in this system. In order to reconcile these two pictures, we build a zero bandwidth multi-orbital Anderson Hamiltonian for the d shell of the transition metal hybridized with the p orbitals of the adjacent nitrogen atoms, by means of maximally localized Wannier function representation of the DFT Hamiltonian. The exact solutions of this model have quantized total spin, without quantized charge at the d shell. We propose that the quantized spin of the models actually belongs to many-body states with two different charge configurations in the d shell, hybridized with the p orbital of the adjacent nitrogen atoms. This scenario implies that the measured spin excitations are not fully localized at the transition metal.

Competition between quantum spin tunneling and Kondo effect

“…The strength of the Kondo coupling is controlled both by Γ and by the departure from the e-h symmetry point, that we change by tuning δ d . Importantly, both the weak coupling picture with step-wise excitations associated with spin transitions, and the strong coupling Kondo regime, are also obtained in the case when the charge on the atom is not quantized, as suggested by DFT calculations [26,27].…”

“…We now consider the effect of valence fluctuations. This effect is particularly important since DFT calculations show that often the average occupation of the d shell is not quantized [26,27]. In our model, we control the valence mixing by shifting the impurity levels by an amount δ d , taking the system out of the e-h symmetry point, leading to deviations from integer occupation number of the impurity shell.…”

“…As we show below, valence fluctuations have a similar effect on the spectra as Kondo exchange. In addition, density functional theory (DFT) calculations show that often charge is not quantized in magnetic adatom systems [26,27].…”

Renormalization of single-ion magnetic anisotropy in the absence of the Kondo effect

“…This can be important since often charge is not quantized in magnetic adatom systems as density functional theory (DFT) calculations show. 26,27 Indeed below I show that charge fluctuations have a similar effect on the electronic spectra and related dI/dV , leading to the renormalization of the spin flip excitations. But in contrast to the renormalization by exchange coupling, the spectra become increasingly asymmetric as the charge fluctuations grow.…”

Probing the Reactivity of Functionalized Surfaces by Porphyrin Metalation

“…We assign these uncommon binding energies to the presence of a much stronger Cl/Cu negative surface dipole as compared to N/Cu (cf. Figure S3); more detailed experimental and theoretical studies of these surface modifications can be found in the literature . After warming up the sample to 300 K, a large shift of all three signatures towards higher BE is observed, specifically: the pyrrolic N1s is shifted by +1.3 eV to 400.2 eV, the iminic N1s peak is shifted by +1.0 eV to 397.8 eV and the C1s peak is shifted by +0.6 eV to 284.3 eV.…”