THESIS
2019
viii, 41 pages : color illustrations ; 30 cm
Abstract
Quantum spin Hall (QSH) insulators are promising candidate for electronic applications, for
their time-reversal protected backscattering-free edge states, with a pair of counterpropagating,
helical electronic modes. Transport experiment has shown monolayer 1T'-WTe
2 displaying
QSH edge modes persisting up to 100 K. Here we present a 4-orbital tight-binding (TB) model for describing the low-energy physics of monolayer WTe
2 in 1T’ structure. Based on
the symmetries analysis and first-principles calculations, ?
x2-?2-type orbitals from 2 M atoms
and ?
x-type orbitals from 2 out of the 4 X atoms are chosen as the basis. Hopping parameters
of the TB model are fitted according to band structure calculated in the density functional
theory (DFT) framework. The TB model includes all the hopp...[
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Quantum spin Hall (QSH) insulators are promising candidate for electronic applications, for
their time-reversal protected backscattering-free edge states, with a pair of counterpropagating,
helical electronic modes. Transport experiment has shown monolayer 1T'-WTe
2 displaying
QSH edge modes persisting up to 100 K. Here we present a 4-orbital tight-binding (TB) model for describing the low-energy physics of monolayer WTe
2 in 1T’ structure. Based on
the symmetries analysis and first-principles calculations, ?
x2-?2-type orbitals from 2 M atoms
and ?
x-type orbitals from 2 out of the 4 X atoms are chosen as the basis. Hopping parameters
of the TB model are fitted according to band structure calculated in the density functional
theory (DFT) framework. The TB model includes all the hopping within nearest neighbor unit
cells. It is able to well reproduce the energy bands −0.3eV to +0.75 eV around Fermi
energy. Edge states for 4 different cuts of nanoribbon along the glide mirror preserving
direction are calculated with Green’s function method, which confirms the nontrivial Z
2
topological phases. The model is easily tunable to capture both semi-metallic and full gapped
scenarios, based on the idea of applying strain on one direction. The TB models developed
here is sufficient to describe the low-energy physics in monolayers 1T'-WTe
2, and they can
serve as basis for further study for their simplicity and high accuracy. The TB model here can
be also easily applied for other monolayer 1T’ transitional metal dichalcogenides MX
2
(M=W, Mo; X=S, Se, Te).
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