A Drastic Change of the Fermi Surface at a Critical Pressure in CeRhIn5: dHvA Study under Pressure

We carried out the de Haas-van Alphen (dHvA) experiment for an antiferromagnet CeRhIn₅ at high pressures up to 3 GPa. The cross-sectional areas of the Fermi surfaces due to main dHvA branches α_i and β₂ at ambient pressure, which are well explained by two kinds of nearly cylindrical Fermi surfaces of a non-4f reference compound LaRhIn₅, are unchanged up to about 2.3 GPa, while the corresponding cyclotron masses m_c^* increase steeply above a pressure P^* = 1.6 GPa where pressure-induced superconductivity sets in : m^*_c = 5.5 m₀ at ambient pressure, 20 m₀ at 1.6 GPa and 60 m₀ at 2.2 GPa for branch β₂, for example. Above 2.4 GPa, new dHvA branches appear, which are in good agreement with the corresponding dHvA branches of a 4f-itinerant heavy fermion superconductor CeCoIn₅, indicating that the 4f electron of CeRhIn₅ becomes itinerant and significantly contributes to the volume of the Fermi surface. The 4f-electron character is thus changed from localized to itinerant at a critical pressure P_c ≃ 2.35 GPa, where the superconducting transition temperature becomes a maximum.