Europhys. Lett.
Volume 68, Number 5, December 2004
Page(s) 685 - 691
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 29 October 2004
Europhys. Lett., 68 (5), pp. 685-691 (2004)
DOI: 10.1209/epl/i2004-10252-0

Kondo behavior of $\chem{U}$ in $\chem{CaB_6}$

G. A. Wigger1, E. Felder1, S. Weyeneth1, H. R. Ott1 and Z. Fisk2

1  Laboratorium für Festkörperphysik, ETH-Hönggerberg - CH-8093 Zürich, Switzerland
2  Department of Physics, University of California - Davis, CA 95616, USA

received 6 July 2004; accepted in final form 30 September 2004
published online 29 October 2004

Replacing $\chem{U}$ for $\chem{Ca}$ in semiconducting $\chem{CaB_6}$ at the few at.% level induces metallic behaviour and Kondo-type phenomena at low temperatures, a rather unusual feature for $\chem{U}$ impurities in metallic hosts. For $\chem{Ca_{0.992}U_{0.008}B_6}$, the resistance minimum occurs at T=17 $\un{K}$. The subsequent characteristic logarithmic increase of the resistivity with decreasing temperature merges into the expected T2-dependence below 0.8 $\un{K}$. Data of the low-temperature specific heat and the magnetization are analyzed by employing a simple resonance-level model. Analogous measurements on $\chem{LaB_6}$ with a small amount of $\chem{U}$ revealed no traces of Kondo behavior, above 0.4 $\un{K}$.

72.15.Qm - Scattering mechanisms and Kondo effect.
75.20.Hr - Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions.
75.30.Mb - Valence fluctuation, Kondo lattice, and heavy-fermion phenomena.

© EDP Sciences 2004