These "light-liked, spin-locked" electrons, called helical Dirac fermions, had been proposed in theory, but never before found in three-dimensional materials. By tuning the electrons to act in this way, the scientists are able to calibrate the surface conductivity of the topological insulator.

"This is a major breakthrough in that they showed how you could control the material to get to the sweet spot [featuring the light-like behavior of electrons] where the surfaces are most interesting," said theoretical physicist Charles Kane of the University of Pennsylvania, who is not affiliated with the research. "Two things had to be done -- first, the bulk of the material had to be made a good insulator, and second, the energy of the surface states had to be adjusted to be precisely at the right point. By tuning the surface to the sweet spot, it opens the door to a whole host of new things you can try to do."

(Phys Org)