ANOMALOUS PEAK EFFECT IN HEAVY-FERMION, INTERMEDIATE-VALENCE AND A15 SUPERCONDUCTORS - EVIDENCE FOR A FULDE-FERRELL-LARKIN-OVCHINNIKOV STATE

An experimental study based upon magnetic and dilatometric measurement s is presented for the clean high-re superconductors UPd2Al3, CeRu2 an d V3Si. All three compounds show an enhanced spin susceptibility. Thei r superconducting state is strongly Pauli limited, and an anomalous pe ak effect is observed at T<(0.8-0.9)T-c, slightly below H-c2(T). This phenomenon appears to be qualitatively consistent with a first-order t ransition between weak and collective pinning, caused by the formation of a staggered order parameter in a generalized Fulde-Ferrell-Larkin- Ovchinnikov phase (M. Tachiki et al., Z. Phys. B, in press).