Disorder driven transition beyond two-component, single-flavor Dirac physics in silicene

We consider the topological insulator (TI) phase of silicene in the presence of an applied electric field E_z perpendicular to its plane. These are assembly of Dirac fermions on a low-buckled 2D hexagonal lattice. The buckled structure generates a staggered sub-lattice potential between silicon atoms at A sites and B sites for the applied field. The starting point of our investigation is the Hamiltonian involving the Dirac kinetic energy, a mass gap term, and the spin-orbit coupling. Tuning of E_z allows for rich behaviour starting from a TI state to a band insulator(BI)with a valley-spin-polarized metal (VSPM) at a critical value in between. As long as the impurity potential strength V₀ is of the same order as the intrinsic spin-orbit coupling (SOC) t_so(∼ 4 meV), VSPM phase is protected. The effective "two-component, single-flavorDirac physics" remains valid in this phase.Theincrease in V₀, however, leads to the disappearance of this phase due to enhanced scattering processes, i.e. the out-of-plane electric field driven topological insulator to metal transition, being predicted for our system, will not be observable when the impurity potential is very high. The enhancement in SOC (t_so) or the Rashbaspin-orbit coupling effect (t₂), however, does not lead to such a scenario. (paper)