Strong paramagnon scattering in single atom Pd contacts

Among all transition metals, palladium (Pd) has the highest density of states at the Fermi energy at low temperatures yet does not fulfill the Stoner criterion for ferromagnetism. However, its close vicinity to magnetism renders it a nearly ferromagnetic metal, which hosts paramagnons, strongly damped spin fluctuations. Here we compare the total and the differential conductance of mono-atomic contacts consisting of single Pd and Cobalt (Co) atoms between Pd electrodes. Transport measurements reveal a conductance for Co of 1\,G0, while for Pd we obtain 2\,G0. The differential conductance of mono-atomic Pd contacts shows a drop with increasing bias, which gives rise to a peculiar \Lambda-shaped spectrum. Supported by theoretical calculations we correlate this finding with the lifetime of hot quasi-particles in Pd which is strongly influenced by paramagnon scattering. In contrast to this, Co adatoms locally induce magnetic order and transport through single cobalt atoms remains unaffected by paramagnon scattering, consistent with theory