Fermi surface instabilities in CeRh2Si2 at high magnetic field and pressure

We present thermoelectric power (TEP) studies under pressure and high magnetic field in the antiferromagnet CeRh2Si2 at low temperature. Under a magnetic field, large quantum oscillations are observed in the TEP, S(H), in the antiferromagnetic phase. They suddenly disappear when entering in the polarized paramagnetic state at H-c, pointing out an important reconstruction of the Fermi surface. Under pressure, S/T increases strongly at low temperature near the critical pressure P-c, where the antiferromagnetic (AF) order is suppressed, implying the interplay of a Fermi surface change and low-energy excitations driven by spin and valence fluctuations. The difference between the TEP signal in the polarized paramagnetic state above H-c at ambient pressure and in the pressure-induced paramagnetic state above P-c can be explained by different Fermi surfaces. Band-structure calculations at P = 0 stress that in the AF phase the 4f contribution at the Fermi level (E-F) is weak, while it is the main contribution in the paramagnetic domain. In the polarized paramagnetic phase the 4f contribution at E-F drops. Large quantum oscillations are observed in the antiferromagnetic state while these disappear in the polarized state above H-c. Comparison is made to the CeRu2Si2 series highly studied for its (H,T) phase diagram.