  We report thermoelectric and resitivity measurements of antiferromagnetic
heavy fermion compound YRh2Si2 at low temperatures down and under high magnetic
field. At low temperature, the thermoelectric power and the resistivity present
several distinct anomalies as a function of field around H_0 ~ 9.5 T when the
magnetic polarization reaches a critical value. The anomalies are accompanied
with a change of sign from negative at low magnetic field to positive at high
field (H>H_0) and are resulting from a Lifshitz-type topological transition of
the Fermi surface. A logarithmic divergence of S/T at T \to 0 K just above H_0
(H=11.5 T) is quite comparable to the well known divergence of S/T in the
temperature range above the antiferromagnetic order at H=0 T referred to as non
Fermi liquid behavior. The transition will be compared to the well
characterized Fermi surface change in CeRu2Si2 at its pseudo-metamagnetic
transition.
