Hybridization gap and dual nature of the heavy-fermion compound UPd$_{2}$Al$_{3}$

We present results from point-contact spectroscopy in the non-superconducting state of UPd$_{2}$Al$_{3}$, a heavy-fermion antiferromagnetic superconductor [1]. Spectroscopic signatures are clearly observed including the distinct asymmetric double-peak structure arising from a hybridization gap opening with the formation of a coherent heavy Fermi liquid. While the hybridization gap is extrapolated to remain finite up to $\sim $28 K, close to the temperature around which the magnetic susceptibility forms a broad peak, the conductance enhancement vanishes at $\sim $18 K, slightly above the antiferromagnetic transition temperature. Our analysis suggests that the conductance enhancement weakens rapidly as the $T_{N}$ is crossed from below because the junction is tuned away from the ballistic regime due to increased scattering off magnons associated with the localized U 5$f$ electrons. This shows that while the hybridization gap opening is not directly associated with the antiferromagnetic ordering, its visibility is greatly affected by the temperature-dependent magnetic excitations. Our results not only support a 5$f$ dual nature scenario proposed for understanding properties of this compound but also shed new light on the interplay between the itinerant and localized electrons. [1] N. Jaggi \textit{et al}., arXiv:1610.08601.