Magnetic and superconducting quantum critical points of heavy-fermion systems

Two examples of heavy-fermion systems are presented : CePd2Si2, an antiferromagnet with a quantum critical point at P-C = 28 kbar and UGe2 an itinerant ferromagnet which transits in a paramagnetic phase above P-C = 16 kbar. In CePd2Si2 the superconductivity domain is centered on P-C. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Neel temperatures. In UGe2 superconductivity appears in 9 kbar at a temperature T-S, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border (P < P-C). Another characteristic temperature T-X is detected by resistivity; the zigzag uranium chain of the lattice may favor a supplementary nesting in the majority spin band. (C) 2001 Elsevier Science B.V. All rights reserved.