Generally, metals, insulators and conventional superconductors tend to have a single type of behavior as far as electricity goes. They can either conduct current or not, and remain consistent in they way they respond to electrical charges.
“The known states of electronic matter are insulators, metals, magnets, semiconductors and superconductors, and each of them has brought us new technology,” explains M. Zahid Hasan.
“Topological superconductors are superconducting everywhere but on the surface, where they are metallic; this leads to many possibilities for applications,” adds the expert.
Here is the abstract from the Nature Physics paper:
Experimental observation of topological order in three-dimensional bulk solids has recently led to a flurry of research activity. Unlike the two-dimensional electron gas or quantum Hall systems, three-dimensional topological insulators can harbour superconductivity and magnetism, making it possible to study the interplay between topologically ordered phases and broken-symmetry states. One outcome of this interplay is the possible realization of Majorana fermions—quasiparticles that are their own antiparticles—on topological surfaces, which is of great interest in fundamental physics. Here we present measurements of the bulk and surface electron dynamics in Bi2Se3 doped with copper with a transition temperature Tc up to 3.8 K, observing its topological character for the first time. Our data show that superconductivity occurs in a bulk relativistic quasiparticle regime where an unusual doping mechanism causes the spin-polarized topological surface states to remain well preserved at the Fermi level of the superconductor where Cooper pairing takes place. These results suggest that the electron dynamics in superconducting Bi2Se3 are suitable for trapping non-Abelian Majorana fermions. Details of our observations constitute important clues for developing a general theory of topological superconductivity in doped topological insulators.
 L.A. Wray et al., Nature Physics v.6, p.855 (2010).