MoTe₂ is a good match for GeI by preserving quantum spin Hall phase

Quantum spin Hall (QSH) insulator is a new class of materials that is quickly becoming mainstream in condensed-matter physics. The main obstacle for the development of QSH insulators is that their strong interactions with substrates make them difficult to study experimentally. In this study, using density functional theory, we discovered that MoTe₂ is a good match for a GeI monolayer. The thermal stability of a van der Waals GeI/MoTe₂ heterosheet was examined via molecular-dynamics simulations. Simulated scanning tunneling microscopy revealed that the GeI monolayer perfectly preserves the bulked honeycomb structure of MoTe₂. The GeI on MoTe₂ was confirmed to maintain its topological band structure with a sizable indirect bulk bandgap of 0.24 eV by directly calculating the spin Chern number to be -1. As expected, the electron mobility of the GeI is enhanced by MoTe₂ substrate restriction. According to deformation-potential theory with the effective-mass approximation, the electron mobility of GeI/MoTe₂ was estimated as 372.7 cm²·s^-1·V^-1 at 300 K, which is 20 times higher than that of freestanding GeI. Our research shows that traditional substrates always destroy the topological states and hinder the electron transport in QSH insulators, and pave way for the further realization and utilization of QSH insulators at room temperature.