Strain-induced topological insulator phase transition in HgSe

Using ab initio electronic structure calculations we investigate the change of the band structure and the nu(0) topological invariant in HgSe (noncentrosymmetric system) under two different types of uniaxial strain along the [001] and [110] directions, respectively. Both compressive [001] and [110] strain lead to the opening of a (crystal field) band gap (with a maximum value of about 37 meV) in the vicinity of Gamma, and the concomitant formation of a camel-back- (inverse camel-back-) shaped valence (conduction) band along the direction perpendicular to the strain with a minimum (maximum) at Gamma. We find that the Z(2) invariant nu(0) = 1 which demonstrates conclusively that HgSe is a strong topological insulator (TI). With further increase of the strain the band gap decreases, vanishing at a critical strain value (which depends on the strain type) where HgSe undergoes a transition from a strong TI to a trivial (normal) insulator. HgSe exhibits a similar behavior under a tensile [110] uniaxial strain. On the other hand, HgSe remains a normal insulator by applying a [001] tensile uniaxial strain. Complementary electronic structure calculations of the nonpolar (110) surface under compressive [110] tensile strain show two Dirac cones at the Gamma point whose spin chiral states are associated with the top and bottom slab surfaces. DOI: 10.1103/PhysRevB.87.075143