Kondo behavior of U in CaB6
Abstract
Replacing U for Ca in semiconducting CaB6 at the few at.% level induces metallic behaviour and Kondo-type phenomena at low temperatures, a rather unusual feature for U impurities in metallic hosts. For Ca 0.992U0.008B6, the resistance minimum occurs at T =17 K. The subsequent, characteristic logarithmic increase of the resistivity with decreasing temperature merges into the expected T 2-dependence below 0.8 K. Data of the low-temperature specific heat and the magnetization are analyzed by employing a simple resonance-level model. Analogous measurements on LaB6 with a small amount of U revealed no traces of Kondo behavior, above 0.4 K.
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