Electronic properties of transition metal atoms on Cu$_2$N/Cu(100)

TL;DR

This study combines DFT and Anderson model calculations to explore the spin excitations of transition metal atoms on Cu$_2$N/Cu(100), revealing that quantized spins arise from many-body states with mixed charge configurations.

Contribution

It introduces a multi-orbital Anderson Hamiltonian derived from DFT to explain the nature of spin excitations and charge states in transition metal adatoms on a surface.

Findings

Average d shell occupation is not quantized.

Quantized total spin emerges from many-body hybridized states.

Measured spin excitations are delocalized, not fully localized at the metal.

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 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.