Quantum Spin Hall States in 2D Monolayer WTe2/MoTe2 Lateral Heterojunctions for Topological Quantum Computation

Abstract

The quantum spin Hall (QSH) states in two-dimensional topological insulators (2DTIs) are expected to be applied to future topological quantum computation. We investigate the two-dimensional (2D) lateral heterojunctions of the monolayer 1T′–WTe2 as a 2DTI and the monolayer 2H–MoTe2 as a topologically trivial insulator using density functional theory. This 2D material is expected to have QSH states at each periodically arranged junction as well as properties distinct from the individual properties of each constituent material. At heterojunctions perpendicular to the dimer chains of W atoms in 1T′–WTe2 (in the y direction), two pairs of helical (QSH) states, one at each junction, connect the valence and conduction bands. The strain induced by the large lattice mismatch of the two materials in the y direction widens the bandgap of the 1T′–WTe2 monolayer as a QSH insulator. In the case of the heterojunctions in the x direction, the difference in atomic structure between the two junctions due to low symmetry creates an energy difference between two helical states and a potential gradient in the wide-bandgap 2H–MoTe2 region, resulting in various junction-localized bands. The widening bandgap of the heterojunctions in the y direction is essential for electronic applications of the QSH states, suggesting that this 2D material, namely, 2D WTe2/MoTe2 heterojunctions, can be a promising candidate for integrating Majorana qubits for future topological quantum computation.