Thermopower of Yb heavy fermion compounds at high pressure

The absolute thermopower S(T) of magnetic and non-magnetic Yb-based heavy fermions compounds was investigated at ambient pressure, High pressure experiments were performed for YbSi (T-N = 1.6 K) and YbCu2Si2. For the latter, which is not magnetically or ordered at P=0, the chemical pressure effect was studied within the solid-solution Yb(NixCu1-x)(2)Si-2 (0 less than or equal to x less than or equal to 1). All S(T)-curves obtained at ambient pressure are characterised by a giant negative peak at a temperature T-min,T-S, and by an additional positive maximum at low temperature for the magnetic compounds. With increasing pressure, S(T-min,T-S) and T-min,T-S. were reduced reflecting a reduction of the Kondo effect. At low temperature a magnetic transition is observed at P>8 GPa in the case of YbCu2Si2 without a sign change in contrast;to the alloys Yb(NixCu1-x)(2)Si-2.