Abstract
Spin-polarized conducting edge currents counterpropagate in quantum spin Hall (QSH) insulators and are protected against disorder-driven localizations by the time-reversal symmetry. Using these spin-currents for device applications require materials having large band gap and fast switchable QSH states. By means of in-depth first-principles calculations, we demonstrate the large band gap and fast switchable QSH state in a newly introduced two-dimensional (2D) material family with 1T^′-MGe₂Z₄ (M = Mo or W and Z = P or As). The thermodynamically stable 1T^′-MoGe₂Z₄ monolayers have a large energy gap around ∼237 meV. These materials undergo a phase transition from a QSH insulator to a trivial insulator with a Rashba-like spin splitting under the influence of an out-of-plane electric field, demonstrating the tunability of the band gap and its band topology. Fast topological phase switching in a large gap 1T^′-MoGe₂Z₄ QSH insulators has potential applications in low-power devices, quantum computation, and quantum communication.