Abstract
Investigation of quantum spin Hall states in 1T' phase of the monolayer transition metal dichalcogenides has recently attracted the attention for its potential in nanoelectronic applications. While most of the theoretical findings in this regard deal with infinitely periodic crystal structures, here we employ density functional theory calculations and k.p Hamiltonian based continuum model to unveil the bandgap opening in the edge-state spectrum of finite width molybdenum disulphide, molybdenum diselenide, tungsten disulphide and tungsten diselenide. We show that the application of a perpendicular electric field simultaneously modulates the band gaps of bulk and edge-states. We further observe that tungsten diselenide undergoes a semi-metallic intermediate state during the phase transition from topological to normal insulator. The tuneable edge conductance, as obtained from the Landauer-Büttiker formalism, exhibits a monotonous increasing trend with applied electric field for deca-nanometer molybdenum disulphide, whereas the trend is opposite for other cases.
Highlights
Investigation of quantum spin Hall states in 1T' phase of the monolayer transition metal dichalcogenides has recently attracted the attention for its potential in nanoelectronic applications
The most subtle feature of this 1T' phase is the inverted bandgap at the Brillouin zone center (Γ), that occurs as a consequence of periodic doubling of transition metal chain, lowering the metal d orbitals below chalcogen p orbitals in the energy scale
The first Brillouin zone (FBZ) has four time-reversal invariant momentum (TRIM) points, labeled in Fig. 1(b) as Γ, X, Y and L, while the fundamental bandgap appears at a point Λ along the kx axis
Summary
Investigation of quantum spin Hall states in 1T' phase of the monolayer transition metal dichalcogenides has recently attracted the attention for its potential in nanoelectronic applications. Based on first principles calculations and tight-binding Hamiltonian, they demonstrated[35] that among several polytypic structures, 1T' phase of a monolayer TMD features band inversion in its bulk energy spectrum It is caused by the formation of periodic doubling of metal chain in 1T' structures and large SOC of www.nature.com/scientificreports transition metals opens a band gap at the otherwise gapless Dirac points. They depicted the edge-state energy spectrum for 1T' MoS2 using surface Green’s function calculations and demonstrated that topological phase transition in these materials can be achieved as a result of external perturbations like electric field or strain. It is found that the edge conductance can be tuned as a function of external electric field only for finite width of the strips, whereas for unconfined geometry it maintains a constant value of e2/h for all electric fields
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