Topological phase transitions of (Bi_xSb_1−x)₂Se₃ alloys by density functional theory

Abstract

We have performed an ab initio total energy investigation of the topological phase transition, and the electronic properties of topologically protected surface states of (BixSb1-x)2Se3 alloys. In order to provide an accurate alloy concentration for the phase transition, we have considered the special quasirandom structures to describe the alloy system. The trivial → topological transition concentration was obtained by (i) the calculation of the band gap closing as a function of Bi concentration (x), and (ii) the calculation of the Z2 topological invariant number. We show that there is a topological phase transition, for x around 0.4, verified for both procedures (i) and (ii). We also show that in the concentration range 0.4 < x < 0.7, the alloy does not present any other band at the Fermi level besides the Dirac cone, where the Dirac point is far from the bulk states. This indicates that a possible suppression of the scattering process due to bulk states will occur.

Tight-binding model for the band dispersion in rhombohedral topological insulators over the whole Brillouin zone

“…In fact, the band structures obtained for several values of t ij b shown in Fig. 5 qualitatively describe the first-principles calculations for Bi 2 (Se 1−x S x ) 3 alloys 35 .…”

Effect of Sb substitution on the topological surface states in Bi2Se3single crystals: a magneto-transport study

“…For x = 0.3, the intercept deviates significantly to a value of 0.875. This could imply [3]. Since the band-gap is expected to reduce with Sb substitution, as mentioned earlier the DP shifts to higher energy with increase in Sb substitution [7].…”

“…Since the end compounds viz., Bi 2 Se 3 and Sb 2 Se 3 are topologically distinct; a topological phase transition is expected to occur at a certain critical concentration (x c ) of Sb substitution. Independent abinitio calculations on the Bi 2-x Sb x Se 3 system by Liu et al [2] and Abdalla et al [3] determined the value of x c = 1.2, corresponding to the alloy composition Bi 0.8 Sb 1.2 Se 3 . However experimentally, the solid solubility of the Sb 2 Se 3 in Bi 2 Se 3 is less than 16 mol% [4] and it is therefore difficult to synthesize single phase crystals with Sb substitution required to observe the phase transition.…”

Controlling Topological States in Topological/Normal Insulator Heterostructures

“…9 (f)) arise due to a symmetry breaking induced by the NI material. It breaks the Bi 2 Se 3 symmetry since the unit cell demands 3 Qls, similar to stacking faults close to the surface [42].…”