Fast Electrically Switchable Large Gap Quantum Spin Hall States in MGe2Z4.

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 requires materials with a large bandgap and fast switchable QSH states. By means of in‐depth first‐principles calculations, this study demonstrates the large bandgap and fast switchable QSH state in a newly introduced 2D material family with 1T′‐MGe2Z4 (M = Mo or W and Z = P or As). These Ge‐based compounds show superior properties with respect to other members of the same family. For the WGe2As4 monolayer it can stabilize the 1T′‐phase, while for the other members of the family, this study needs an appropriate strain. The dynamically stable 1T′‐MGe2Z4 monolayers have a large energy gap up to 237 meV for WGe2As4. 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 a fast tunability of the bandgap and its band topology for the Ge‐based compounds. Fast topological phase switching in a large gap 1T′‐MGe2Z4 QSH insulators have potential applications in low‐power devices, quantum computation, and quantum communication. [ABSTRACT FROM AUTHOR]