Pd/Cu Site Interchange and Non-Fermi-Liquid Behavior in UCu_4Pd

TL;DR

This study uses X-ray-absorption measurements to reveal lattice disorder and site interchange in UCu_4Pd, linking these structural features to its non-Fermi-liquid behavior through a Kondo disorder model.

Contribution

It provides direct evidence of Pd-Cu site interchange and links local structural disorder to non-Fermi-liquid behavior using a quantitative Kondo disorder model.

Findings

24% Pd atoms occupy Cu sites

Lattice disorder correlates with non-Fermi-liquid behavior

Kondo disorder model matches susceptibility data

Abstract

X-ray-absorption fine-structure measurements of the local structure in UCu_4Pd are described which indicate a probable lattice-disorder origin for non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed, consistent with 24 +/- 3% of the Pd atoms occupying nominally Cu sites. A "Kondo disorder" model, based on the effect on the local Kondo temperature T_K of this interchange and some additional bond-length disorder, agrees quantitatively with previous experimental susceptibility data, and therefore also with specific heat and magnetic resonance experiments.