Dimensional engineering of a topological insulating phase in Half-Heusler LiMgAs

Abstract

Abstract We propose a novel technique of dimensional engineering to realize low dimensional topological insulator from a trivial three dimensional parent. This is achieved by confining the bulk system to one dimension along a particular crystal direction, thus enhancing the quantum confinement effects in the system. We investigate this mechanism in the Half-Heusler compound LiMgAs with face-centered cubic (FCC) structure. At ambient conditions the bulk FCC structure exhibits a semi-conducting nature. But, under the influence of high volume expansive pressure (VEP) the system undergoes a topological phase transition (TPT) from semi-conducting to semi-metallic forming a Dirac cone. At a critical VEP we observe that, spin-orbit coupling (SOC) effects introduce a gap of $$\sim$$ ∼ 1.5 meV in the Dirac cone at high symmetry point $$\Gamma$$ Γ in the Brillouin zone. This phase of bulk LiMgAs exhibits a trivial nature characterized by the $${\mathbb {Z}}_2$$ Z 2 invariants as (0,000). By further performing dimensional engineering, we cleave [111] plane from the bulk FCC structure and confine the system in one dimension. This low-dimensional phase of LiMgAs has structure similar to the two dimensional $${\text {1T-MoS}}_2$$ 1T-MoS 2 system. Under a relatively lower compressive strain, the low-dimensional system undergoes a TPT and exhibits a non-trivial topological nature characterized by the SOC gap of $$\sim$$ ∼ 55 meV and $${\mathbb {Z}}_2$$ Z 2 invariant $$\nu$$ ν = 1. Although both, the low-dimensional and bulk phase exhibit edge and surface states, the low-dimensional phase is far more superior and exceptional as compared to the bulk parent in terms of the velocity of Fermions ( $${\text {v}}_f$$ v f ) across the surface states. Such a system has promising applications in nano-electronics.