A tunable topological insulator in the spin helical Dirac transport regime

Topological insulators: tuned to protection Helical Dirac fermions are relativistic particles which, unlike conventional Dirac fermions in graphene, have a net intrinsic angular momentum (spin) interlocked with their translational momentum, a property desirable for spintronic and computing technologies. Recently, it was proposed that such helical Dirac systems could be realized in so-called topological insulators — materials in which strong spin–orbit coupling gives rise to a bulk insulating gap and surface states protected against scattering by time-reversal symmetry. Hsieh et al. combine spin- and momentum-resolved spectroscopic imaging techniques to report the experimental realization of such a system in a bismuth-based material, where the experiments reveal nearly 100% spin polarization even up to room temperature. Crucially, the paper reports tunability of the fermion density, via doping, enabling the authors to drive the system to the so-called topological transport regime, which is believed to facilitate spin transport without heat dissipation.