Kondo decoherence: finding the right spin model for iron impurities in gold and silver

TL;DR

This study uses electron decoherence measurements and theoretical calculations to identify the appropriate spin model for Fe impurities in gold and silver, concluding that a spin-3/2 Kondo model best describes the system.

Contribution

The paper combines density functional theory and experimental data with numerical renormalization group analysis to determine the correct spin value for Fe impurities, resolving a longstanding ambiguity.

Findings

Density functional theory suggests S=3/2 for Fe impurities.

Experimental data aligns with S=3/2 predictions.

The S=3/2 Kondo model accurately describes decoherence and resistivity measurements.

Abstract

We exploit the decoherence of electrons due to magnetic impurities, studied via weak localization, to resolve a longstanding question concerning the classic Kondo systems of Fe impurities in the noble metals gold and silver: which Kondo-type model yields a realistic description of the relevant multiple bands, spin and orbital degrees of freedom? Previous studies suggest a fully screened spin $S$ Kondo model, but the value of $S$ remained ambiguous. We perform density functional theory calculations that suggest $S = 3/2$. We also compare previous and new measurements of both the resistivity and decoherence rate in quasi 1-dimensional wires to numerical renormalization group predictions for $S=1/2,1$ and 3/2, finding excellent agreement for $S=3/2$.