Optical investigations of the electrodynamics of UPd 2 AI 3

We have investigated the electrodynamic response of UPd2AIs. At low temperatures, we observe the formation of a low-frequency narrow resonance, which indicates the development of the many-body coherent state. We do not find any evidence of a gap absorption associated to a spin density wave state below the antiferromagnetic phase transition at TN = 14 K, which would develop as a consequence of a Fermi surface instability. The heavy Fermion superconductor U Pd2Als is one of the fascinating materials, besides URu,Si2 and UNizAIs ~ 10 ° [ 1, 2], showing the coexistence of both superconductivity and magnetic ordering [3]. The dc magnetic susceptibilO ity exhibits a kink at Ts = !4 K and a remarkable drop at about T'~ = 2 K, where also the specific heat shows clear anomalies. " ~ The DC resistivity pl TI shown in Fig. 1 bears a close ['-' similarity with the transport properties of other heavy Fermions. Above the broad maximum at T~o = 80 K, >', .,.a p(T} decreases witla increasing temperature in a manner "~ similar to that observed in metals containing isolated ~ iO -I tmtgnetic impurities, suggesting a Kondo scattering .~ or] mechanism. Below the coherence tempera:ure T,,. where ¢~ the many-body effects progres:;ively derek, p, there is first the antifcrromagnctic transition at Tx = 15 K, which reflects the ftecziag out of spin disorder scattering, and then a sharp drop :o zero at the superconducting transition T, :--1.7 K. While in URu,Si: the antifer* ('orre,,ponding author. UPdzA1 a