Prediction of flatness-driven quantum spin Hall effect in functionalized germanene and stanene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• The search for materials exhibiting the quantum spin Hall (QSH) effect at room temperature is ongoing.
• Compatibility with existing group-IV electronics is a key requirement for practical applications.

Purpose of the Study:

• To predict and identify new two-dimensional (2D) materials with robust room-temperature QSH properties.
• To explore the tunability of QSH effects in functionalized germanene and stanene.

Main Methods:

• First-principles calculations were employed to investigate the electronic and topological properties of functionalized germanene and stanene (f-GeX2 and f-SnX2).
• The effects of structural modifications (flattening, functionalization with X = H, F, Cl, Br, I) and mechanical strain on the QSH phases were analyzed.
• The influence of spin-orbit coupling (SOC) and substrate interactions (BN) on the electronic band structure and edge states was examined.

Main Results:

• A new class of QSH phases was predicted in flattened germanene and stanene (f-GeX2 and f-SnX2) with a significant bulk band gap up to 0.56 eV.
• Structural flatness induced an inverted band order without SOC, which was then gapped by SOC, a distinct behavior from buckled counterparts.
• Enhanced Fermi velocity of edge states was observed with edge modification.
• The nontrivial QSH state and Dirac cone were preserved when films were deposited on a BN substrate.

Conclusions:

• Flattened germanene and stanene functionalized with X atoms represent a promising platform for realizing the room-temperature quantum spin Hall effect.
• These materials offer tunable electronic properties and compatibility with group-IV electronics.
• The findings provide a pathway for developing next-generation topological electronic devices.