Prediction of tetragonal monolayer CuN with a quantum spin Hall state

Abstract

Abstract Two-dimensional (2D) quantum spin Hall (QSH) insulator are promising candidates for miniaturized electronic and dissipationless transport devices. The bottleneck preventing applications from QSH phase, however, is lack of feasible 2D materials in experiments so far. By using first-principles calculations, here we propose a realistic 2D QSH phase in tetragonal CuN, which is dynamically and mechanically stable. Band structure analysis reveals that it is a nontrivial QSH phase robust against external strains. The origin of QSH effect can be identified by a px-pz band inversion, topological invariant Z2, and helical edge states within the bulk gap. Also, a heterostructure composed of CuN deposited on semiconducting AlAs substrate remains topologically nontrivial with a sizable gap. These findings provide a promising platform to design new QSH insulators in tetragonal lattices, which show potential applications in multifunctional spintronics devices.