Quantum phase transition in the disordered topological insulator (Bi_1-xSb_x)₂Se₃

First principles-based studies[1] have predicted that the disordered substitutional alloy (Bi_1-xSb_x)₂Se₃ undergoes a topological phase transition beyond a critical value of impurity concentration due to the decrease of the Spin-Orbit interaction. In their calculations, different methods yielded different values for the critical impurity concentration, which motivates us to perform systematic DFT-based simulations to study the topological phase transition. We perform simulations initially of x = 25, 50 and 75 percent Sb, including van der Waals interactions, with the goal of identifying the transition and analyzing the structural and electronic properties near the critical impurity concentration. To mimic substitutional disorder, we have constructed partially ordered supercells where the atomic pair correlations are zero up to the third nearest neighbor cell.

[1] J. Liu and D. Vanderbilt, Phys. Rev. B 88, 224202 (2013)