The quasilinear bands in the topologically trivial skutterudite insulator ${\mathrm{CoSb}}_3$ are studied under adiabatic, symmetry-conserving displacement of the Sb sublattice. In this cubic, time-reversal and inversion symmetric system, a transition from trivial insulator to topological point Fermi surface system occurs through a critical point in which massless (Dirac) bands appear, and moreover are degenerate with massive bands. Spin-orbit coupling, while small due to the type of band character, coupled with tetragonal strain opens the gap required to give the topological insulator. The mineral skutterudite (${\mathrm{CoSb}}_3$) is very near the critical point in its natural state.

• Received 23 July 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.056401