Heavy fermion state and quantum criticality

Abstract

The heavy fermion state in the f -electron systems is due to competition between the RKKY interaction and the Kondo effect. The typical compound is CeCu 6 . To understand the electronic state, we studied the Fermi surface properties via the de Haas-van Alphen (dHvA) experiments and energy band calculations for CeSn 3 , CeRu 2 Si 2 , UPt 3 , and nowadays, transuranium compounds of NpGe 3 and PuIn 3 , together with YbCu 2 Si 2 . Pressure is also an important technique to control the electronic state. For example, the Néel temperature T N decreases with increasing pressure P and becomes zero at the critical pressure P c : T N → 0 for P → P c . The typical compound is an antiferromagnet CeRhIn 5 , which we studied from the dHvA experiment under pressure. A change of the 4 f -electronic state from localized to itinerant is realized at P c ≃ 2.4 GPa , revealing the first-order phase transition, together with a divergent tendency of the cyclotron mass at P c . It is stressed that appearance of superconductivity in CeRhIn 5 is closely related to the heavy-fermion state. It is also noted that the parity-mixed novel superconducting state might be realized in a pressure-induced superconductor CeIrSi 3 without inversion symmetry in the crystal structure.