Fast Electrically Switchable Large Gap Quantum Spin Hall States

Adv. Electron. Mater. 2023, 2300156

(a) Spin-polarized topological edge states of MoGe2P4 are shown in red and blue for spin-up and spin-down, respectively. The zero line marks the Fermi level. (b) Schematic representation of the counterpropagating spin channels in the Quantum Spin Hall effect. The spin-up and spin-down electrons are represented as red and blue balls, respectively. (c) Topological invariant Z2 and bandgap of MoGe2P4 as a function of the applied out-of-plane electric field. The critical electric force fields qEC=±0.077 eV Å-1 are marked with vertical dashed lines.

Spin-polarised conducting edge currents, flowing in opposite directions in a spin quantum Hall (QSH) insulator, are protected by time-reversal symmetry from disorder-induced localisation. Using these spin-currents for device applications requires materials with a large bandgap and fast switchable QSH states.

Employing in-depth first-principles calculations, IFPAN researchers Carmine Autieri, Rajibul Islam, Ghulam Hussain in collaboration with other theory groups have demonstrated the presence of just such a large bandgap and fast switchable QSH states 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 requires 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.

Publications

Fast Electrically Switchable Large Gap Quantum Spin Hall States in MGe2Z4

Rajibul Islam, Ghulam Hussain, Rahul Verma, Mohammad Sadegh Talezadehlari, Zahir Muhammad, Bahadur Singh, and Carmine Autieri

Adv. Electron. Mater. 2023, 2300156

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