Study of energy scales in Lu1-xYbxRh2Si2

In strongly correlated f-electron systems, Kondo interaction and crystal electric field (CEF) excitations often give rise to large anomalies in the thermopower. Thermopower investigations are therefore known to be a useful tool to determine the Kondo and CEF energy scales. Measurements of the thermopower of the stoichiometric heavy fermion system YbRh2Si2 revealed a single large minimum around 80 K which was attributed to both, Kondo interaction and CEF effects. From the obtained data no separation of Kondo and CEF energy scales was possible. We performed thermopower measurements on the diluted heavy fermion system Lu1-xYbxRh2Si2. For Yb concentrations of x≤0.5 the pronounced thermopower minimum splits into 2 separate features. An extrapolation of the position of the low temperature shoulder allows to deterne the Kondo temperature of pure YbRh2Si2 (TK∼25 K). Our data suggest a strong dependence of the minima on the Yb concentration x that may not be solely attributed to the extremely small unit cell volume change. We compare our results to theoretical calculations of the high temperature thermopower of Yb intermetallics including both, CEF splitting and charge fluctuations. (orig.)