First-principles study of transition-metal doped GaBiCl2 monolayers as magnetic topological insulators

Abstract

Magnetic topological insulators (MTIs) offer a pathway to dissipationless quantum and spintronic devices, but to date, their realization has been limited to extremely low temperatures. Therefore, identifying MTIs with sizable band gaps is crucial for raising the operating temperature toward practical applications. Through first-principles calculations, we present the first systematic study of transition-metal-doped GaBiCl₂ monolayers (X = Cu, Mn, Cr, and Mo) as a platform for high-temperature topological phases. We find that Cr doping induces a magnetic topological semimetal (MTSM), where strong Cr-3d/host hybridization collapses the global gap. In contrast, Mo doping stabilizes a ferromagnetic MTI with a nontrivial invariant and a robust spin–orbit coupling-induced band gap of 41.3 meV, indicating its potential for room temperature applications. The preservation of the nontrivial gap arises from relatively weak p–d hybridization between Mo-4d and host Bi-p states, which suppresses the impurity-driven gap closure seen with other dopants. These results make Mo-doped GaBiCl₂ a promising candidate for room temperature MTIs and a versatile platform for exploring the quantum anomalous Hall effect and next-generation spintronic devices.