ENHANCEMENT OF MAGNETIC FLUCTUATIONS ON PASSING BELOW T-C IN THE HEAVY-FERMION SUPERCONDUCTOR UPD2AL3

The heavy fermion superconductor UPd2Al3 exhibits the unusual combinat ion of an antiferromagnetic phase transition, at T-N = 14.3 K, followe d by a superconducting phase transition below 2 K without destruction of the ordered magnetic moment. Polarized inelastic neutron scattering reveals the presence of two coupled modes, both transverse to the sub lattice magnetization. On Passing into the superconducting phase an ab rupt change is observed in the magnetic inelastic response. We show th at it is reasonable to consider the superconducting state as arising o ut of interactions between quasiparticles which are strongly renormali zed by the low-frequency exchange field.