The dilute limit of heavy fermions: evidence of the coherent nature of CeAl3

Strongly diluted CexLa1-xAl3 alloys have been studied by the low temperature specific heat in order to elucidate the mechanism that determines their ground state. The results for alloys with Ce concentrations of 0.0005≤x≤0.1 are fairly consistent with a S = 1/2 Kondo behavior. However, the single-ion scaling is observed only below x = 0.01. The true single-ion Kondo temperature is small, 0.2 K, approximately equal to that for dilute CeAl2. It is about 20 times smaller than that for CeAl3, indicating the coherent nature of CeAl3. The single-ion contribution to thermodynamic properties of CeAl3 is negligible even at temperatures as high as 5 K.