Excitation spectra of transition metal atoms on the Ag (100) surface controlled by Hund's exchange

TL;DR

This study combines photoemission experiments and first-principles calculations to analyze how Hund's exchange influences the excitation spectra of transition metal atoms on Ag(100), revealing non-monotonous spectral evolution.

Contribution

It demonstrates the dual role of Hund's exchange in affecting spectral splittings and charge fluctuations across the 3d series of transition metals on a surface.

Findings

Spectral splittings decrease with 3d shell filling.

Charge fluctuations and quasiparticle weight vary non-monotonously.

Hund's exchange significantly influences spectral features.

Abstract

We report photoemission experiments revealing the valence electron spectral function of Mn, Fe, Co and Ni atoms on the Ag(100) surface. The series of spectra shows splittings of higher energy features which decrease with the filling of the 3d shell and a highly non-monotonous evolution of spectral weight near the Fermi edge. First principles calculations demonstrate that two manifestations of Hund's exchange $J$ are responsible for this evolution. First, there is a monotonous reduction of the effective exchange splittings with increasing filling of the 3d shell. Second, the amount of charge fluctuations and, thus, the weight of quasiparticle peaks at the Fermi level varies non-monotonously through this 3d series due to a distinct occupancy dependence of effective charging energies $U_{\rm eff}$.