  Realization of topological superconductors (TSCs) hosting Majorana fermions
is a central challenge in condensed-matter physics. One approach is to use the
superconducting proximity effect (SPE) in heterostructures, where a topological
insulator contacted with a superconductor hosts an effective p-wave pairing by
the penetration of Cooper pairs across the interface. However, this approach
suffers a difficulty in accessing the topological interface buried deep beneath
the surface. Here, we propose an alternative approach to realize topological
superconductivity without SPE. In a Pb(111) thin film grown on TlBiSe2, we
discover that the Dirac-cone state of substrate TlBiSe2 migrates to the top
surface of Pb film and obtains an energy gap below the superconducting
transition temperature of Pb. This suggests that a BCS superconductor is
converted into a TSC by the topological proximity effect. Our discovery opens a
route to manipulate topological superconducting properties of materials.
