The coordination dependence of electric-field gradients and hyperfine fields at 5sp impurities on fcc metal surfaces

TL;DR

This paper compares ab initio calculations with experimental data on electric-field gradients and hyperfine fields of Cd impurities on fcc metal surfaces, revealing underlying systematic behaviors and explaining variations in hyperfine fields.

Contribution

It demonstrates a unified systematic behavior of electric-field gradients and hyperfine fields across different surface orientations and provides a microscopic explanation for the observed dependencies.

Findings

The systematic rule for surface site assignment applies to all surface orientations when viewed systematically.

The parabolic coordination dependence of hyperfine fields at Ni surfaces is a general trend, with notable deviations.

Different 5sp impurities exhibit unique coordination dependencies explained by s-DOS near the Fermi level.

Abstract

We present a comparison between accurate \textit{ab initio} calculations and a high-quality experimental data set (1986-2002) of electric-field gradients and magnetic hyperfine fields of Cd at different sites on Ni, Cu, Pd and Ag surfaces. Experiments found a systematic rule to assign surface sites on (100) and (111) surfaces based on the main component of the electric-field gradient, a rule that does not work for (110) surfaces. Our calculations show that this particular rule is a manifestation of a more general underlying systematic behavior. When looked upon from this point of view, (100), (111) \emph{and} (110) surfaces behave in precisely the same way. The experimentally observed parabolic coordination number dependence of the Cd magnetic hyperfine field at Ni surfaces is verified as a general trend, but we demonstrate that individual cases can significantly deviate from it. It is shown that the hyperfine fields of other 5sp impurities at Ni surfaces have their own, typical coordination number dependence. A microscopic explanation for the different dependencies is given in terms of the details of the s-DOS near the Fermi level.