  Majorana fermions are predicted to localize at the edge of a topological
superconductor, a state of matter that can form when a ferromagnetic system is
placed in proximity to a conventional superconductor with strong spin-orbit
interaction. With the goal of realizing a one-dimensional topological
superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the
surface of superconducting lead (Pb). Using high-resolution spectroscopic
imaging techniques, we show that the onset of superconductivity, which gaps the
electronic density of states in the bulk of the Fe chains, is accompanied by
the appearance of zero energy end states. This spatially resolved signature
provides strong evidence, corroborated by other observations, for the formation
of a topological phase and edge-bound Majorana fermions in our atomic chains.
