Drastic change of the electronic states at the quantum critical point in heavy fermions

We studied the change of the Fermi surface properties in antiferromagnets CeIn₃ and CeRhIn₅ via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P_c, where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn₃ and CeRhIn₅ at P_c. Namely, the 4f-electron contributes to the volume of the Fermi surface above P_c. Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P_c, where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt₃ Si and CeTX₃ (T:Co, Ir, Rh, X:Si, Ge). The spin-orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair.