Metacinnabar ({\beta}-HgS): a strong 3D topological insulator with   highly anisotropic surface states
  We establish the presence of topologically protected edge states on the (001) surface of HgS in the zinc-blende structure using density-functional electronic structure calculations. The Dirac point of the edge state cone is very close to the bulk valence band maximum. The Dirac cone is extremely anisotropic with a very large electron velocity along one diagonal of the surface elementary cell x' and a nearly flat dispersion in the perpendicular direction y'. The strong anisotropy originates from a broken fourfold rotoinversion symmetry at the surface. 
Franc\c{o}is Virot, Roland Hayn, Manuel Richter, and Jeroen van den   Brink
cond-mat.mtrl-sci