  Gold surfaces host special electronic states that have been understood as a
prototype of Shockley surface states (SSs). These SSs are commonly employed to
benchmark the capability of angle-resolved photoemission spectroscopy (ARPES)
and scanning tunneling spectroscopy. We find that these Shockley SSs can be
reinterpreted as topologically derived surface states (TDSSs) of a topological
insulator (TI), a recently discovered quantum state. Based on band structure
calculations, the Z2 topological invariant can be well defined to characterize
the nontrivial features of gold that we detect by ARPES. The same TDSSs are
also recognized on surfaces of other well-known noble metals (e.g., silver,
copper, platinum, and palladium). Besides providing a new understanding of
noble metal SSs, finding topological states on late transition metals provokes
interesting questions on the role of topological effects in surface-related
processes, such as adsorption and catalysis.
