Magnetic field driven electronic singularities through metamagnetic phenomena: Case of the heavy fermion antiferromagnet Ce(Ru_0.92Rh _0.08)₂Si₂

Thermoelectric power measurements on the heavy fermion antiferromagnet Ce(Ru_0.92Rh_0.08)₂Si₂ under magnetic field (H) show clearly that the antiferromagnetic state below the critical field Hc ∼ 2:8 T can be fully decoupled from the pseudo-metamagnetic crossover at H_m ∼ 5:8 T which occurs when the magnetization reaches a critical value. By contrast to the weak field variation of the Sommerfeld coefficient of the specific heat in the field window from Hc to H_m, two electronic singularities with opposite signs are detected in the thermoelectric power. The interplay between the magnetic instability and the topological change of the Fermi surface is discussed and we argue similarities to other field instabilities in various heavy fermion compounds.