The topological insulator and a parasitic metal - friends or foes?

In the flurry of experiments looking for topological insulator

materials, it has been recently discovered that some bulk metals very

close to topological insulator electronic states support the same

topological surface states that are the defining characteristic of the

topological insulator. First observed in spin-polarized angle resolved

photoemission spectroscopy (ARPES) in Sb [D. Hsieh et al., Science

323, 919 (2009)], the helical surface states in the metallic systems

appear to be robust to at least mild disorder. We present here a

theoretical investigation of the nature of these “helical metals”—bulk

metals with helical surface states. We explore how the surface and

bulk states can mix, in both clean and disordered systems, as well as

discuss possible magnetoelectric coupling phenomena.