  Many-body phenomena are paramount in physics. In condensed matter, their
hallmark is considerable on a wide range of material characteristics spanning
electronic, magnetic, thermodynamic and transport properties. They potentially
imprint non-trivial signatures in spectroscopic measurements, such as those
assigned to Kondo, excitonic and polaronic features, whose emergence depends on
the involved degrees of freedom. Here, we address systematically zero-bias
anomalies detected by scanning tunneling spectroscopy on Co atoms deposited on
Cu, Ag and Au(111) substrates, which remarkably are almost identical to those
obtained from first-principles. These features originate from gaped
spin-excitations induced by a finite magnetic anisotropy energy, in contrast to
the usual widespread interpretation relating them to Kondo resonances. Resting
on relativistic time-dependent density functional and many-body perturbation
theories, we furthermore unveil a new many-body feature, the spinaron,
resulting from the interaction of electrons and spin-excitations localizing
electronic states in a well defined energy.
