  We present results from point-contact spectroscopy of the antiferromagnetic
heavy-fermion superconductor UPd$_2$Al$_3$: conductance spectra are taken from
single crystals with two major surface orientations as a function of
temperature and magnetic field, and analyzed using a theory of co-tunneling
into an Anderson lattice. Spectroscopic signatures are clearly identified
including the distinct asymmetric double-peak structure arising from the
opening of a hybridization gap when a coherent heavy Fermi liquid is formed.
Both the hybridization gap, found to be 7.2 $\pm$ 0.3 meV at 4 K, and the
conductance enhancement above a flat background decrease upon increasing
temperature. While the hybridization gap is extrapolated to remain finite up to
$\sim$28 K, close to the temperature around which the magnetic susceptibility
displays a broad peak, the conductance enhancement vanishes at $\sim$18 K,
slightly above the antiferromagnetic transition temperature ($T_\textrm{N}$
$\approx$ 14 K). This rapid decrease of the conductance enhancement is
understood as a consequence of the junction drifting 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 in the
conductance is greatly affected by the temperature-dependent magnetic
excitations. Our findings are not only consistent with the 5$f$ dual-nature
picture in the literature but also shed new light on the interplay between the
itinerant and localized electrons in UPd$_2$Al$_3$.
