Abstract
Recently, searching large-bulk band gap topological insulator (TI) is under intensive study. Through k·P theory and first-principles calculations analysis on antimonene, we find that α-phase antimonene can be tuned to a 2D TI under an in-plane anisotropic strain and the magnitude of direct bulk band gap (SOC gap) depends on the strength of spin-orbit coupling (SOC) which is strain-dependent. As the band inversion of this TI accompanies with an indirect band gap, the TI bulk band gap is the indirect band gap, not the SOC gap. SOC gap can be enhanced by increasing strain, whereas the indirect band gap can be closed by increasing strain, such that large bulk band gap are forbidden. With the k·P theory analysis on antimonene, we know how to avoid such an indirect band gap. In case of indirect band gap avoided, the SOC gap could become the bulk band gap of a TI which can be enhanced by strain. Thus our theoretical analysis can help searching large bulk band gap TI.
Highlights
In the past 10 years, topological insulator phase has emerged in condensed matter physics with theoretical predictions and experimental observations of this phase in real materials [1–32]
The first-principles calculation results of strained αphase antimonene shows that strain can induce topological insulator (TI) phase on antimonene and can enhance the magnitude of TI’s direct bulk band gap (SOC gap), such that the magnitude of the spin-orbit coupling (SOC) gap no longer depends on the atomic order only
In this paper, we analyze antimonene with k · P theory and find that without considering SOC, strain-induced point band inversion would cause band crossing between VBM and CBM and the system turns into metallic state
Summary
In the past 10 years, topological insulator phase has emerged in condensed matter physics with theoretical predictions and experimental observations of this phase in real materials [1–32]. Through k · P theory, we learn that, in an anisotropic system, the band inversion of a TI phase transition will accompany with an indirect band gap if VBM and CBM cannot couple to each other by non-SOC k · P term Such a theoretical and numerical analysis makes it clear how the strain tunes the SOC gap of a TI and the cause of the indirect band gap. It can help applying such a mechanism on other materials to achieve the goal of searching large bulk band gap TI among light atoms to meet the requirement of spintronic devices with low prices. Isotropic or anisotropic strain changes lattice constant and the structure parameters, but the crystal structure symmetry remains the same
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