Fermi surface instability in CeRh₂Si₂ under pressure

That the 4f electrons in the rare-earth antiferromagnetic compound CeRh₂Si₂ should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas-van Alphen experiment to the result of energy band calculations for LaRh₂Si₂. When pressure p is applied to the compound, the Néel temperature T_NI=36 K decreases and finally becomes zero at p_c≃1.0-1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the 4f-itinerant-band model. The corresponding cyclotron mass is large, being about 22m₀.