Behaviour of thermopower at the transition from impurity Kondo towards heavy fermion regime in CexLa1-xCu2.05Si2

We report electrical resistivity and thermopower measurements of the CexLa1-xCu2.05Si2 alloy system from 2 to 300 K. Up to x = 0.50 the thermopower is positive in the whole temperature range and the system shows the characteristics of the impurity Kondo regime. It is interesting that at the onset of coherence observed in the resistivity at x = 0.70 one can observe a giant and negative thermopower at low temperatures, which is a characteristic of the classical Kondo lattice system CeCu2Si2. The results show, among others, that the thermopower feels the transition to the coherent HF state at lower concentrations than the resistivity. (C) 1999 Elsevier Science B.V. All rights reserved.