Strong suppression of superconductivity by divalent Ytterbium Kondo-holes in CeCoIn_5

TL;DR

This study demonstrates that divalent Yb-ions act as Kondo-holes in CeCoIn_5 epitaxial films, strongly suppressing superconductivity and Kondo coherence, contrasting with bulk crystal results and highlighting the advantages of thin film studies.

Contribution

It provides new insights into the impurity effects of Yb-ions in Kondo lattices using epitaxial thin films, revealing their role as nonmagnetic scatterers and challenging previous bulk crystal findings.

Findings

Yb-substitution causes linear decrease in unit cell volume

Yb-ions act as nonmagnetic impurity scatterers

Superconductivity is strongly suppressed by Yb-ions

Abstract

To study the nature of partially substituted Yb-ions in a Ce-based Kondo lattice, we fabricated high quality Ce_{1-x}Yb_xCoIn_5 epitaxial thin films using molecular beam epitaxy. We find that the Yb-substitution leads to a linear decrease of the unit cell volume, indicating that Yb-ions are divalent forming Kondo-holes in Ce_{1-x}Yb_xCoIn_5, and leads to a strong suppression of the superconductivity and Kondo coherence. These results, combined with the measurements of Hall effect, indicate that Yb-ions act as nonmagnetic impurity scatters in the coherent Kondo lattice without serious suppression of the antiferromagnetic fluctuations. These are in stark contrast to previous studies performed using bulk single crystals, which claim the importance of valence fluctuations of Yb-ions. The present work also highlights the suitability of epitaxial films in the study of the impurity effect on the Kondo lattice.