  Magnetic impurities deposited on topological superconductor candidate PbTaSe2
can introduce a non-splitting zero-energy state inside the superconducting gap,
which has been proposed as a field-free platform for topological zero modes.
However, it is still unclear how robust the topological state in PbTaSe2 is
against magnetic impurities, which is related to the topological nature of the
zero-energy state as well as its potential for quantum computation. In this
work, we use scanning tunneling microscopy (STM) to study the topological
surface state in the normal state of PbTaSe2 under the perturbation of magnetic
impurities. We visualize the quasi-particle interference (QPI) arising from the
topological surface state. We then deposit Fe impurities on the surface to form
atomic Fe adatoms. We find that each Fe adatom sits at a unique interstitial
position on the surface and features a local state at high energies, both of
which are consistent with our first-principles calculation that further reveals
its large magnetic moment. Our systematic Fe deposition and subsequent
measurements show that the arc-like QPI pattern at the Fermi energy is robust
with up to 3% Fe coverage where the atomic nature of Fe adatoms still holds.
Our results provide evidence that the topological surface state at the Fermi
energy in PbTaSe2 is robust against dilute magnetic impurities.
