  Yu-Shiba-Rusinov (YSR) bound states appear when a magnetic atom interacts
with a superconductor. Here, we report on spin-resolved spectroscopic studies
of YSR states related with Fe atoms deposited on the surface of the topological
superconductor FeTe0.55Se0.45 using a spin-polarized scanning tunneling
microscope. We clearly identify the spin signature of pairs of YSR bound states
at finite energies within the superconducting gap having opposite spin
polarization as theoretically predicted. In addition, we also observe
zero-energy bound states for some of the adsorbed Fe atoms. In this case, a
spin signature is found to be absent indicating the absence of Majorana bound
states associated with Fe adatoms on FeTe0.55Se0.45.
