Tunable giant spin hall conductivities in a strong spin-orbit semimetal: Bi(1-x) Sb(x).

Intrinsic spin Hall conductivities are calculated for strong spin-orbit Bi(1-x)Sb(x) semimetals, from the Kubo formula and using Berry curvatures evaluated throughout the Brillouin zone from a tight-binding Hamiltonian. Nearly crossing bands with strong spin-orbit interaction generate giant spin Hall conductivities in these materials, ranging from 474 (ℏ/e)(Ω  cm)^{-1} for bismuth to 96 (ℏ/e)(Ω  cm)^{-1} for antimony; the value for bismuth is more than twice that of platinum. The large spin Hall conductivities persist for alloy compositions corresponding to a three-dimensional topological insulator state, such as Bi(0.83)Sb(0.17). The spin Hall conductivity could be changed by a factor of 5 for doped Bi, or for Bi(0.83)Sb(0.17), by changing the chemical potential by 0.5 eV, suggesting the potential for doping or voltage tuned spin Hall current.