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 CeIn 3 and CeRhIn 5 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 CeIn 3 and CeRhIn 5 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 CePt 3 Si and CeTX 3 (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.