Magnetic proximity engineering of massive Dirac fermions in a CrI₃/Bi₂Se₃ van der Waals heterostructure

Magnetic proximity provides a disorder-free route to break time-reversal symmetry in topological insulators and to generate massive Dirac fermions. In this work, we investigate proximity-induced magnetic effects in a CrI₃/Bi₂Se₃ van der Waals heterostructure using first-principles calculations that incorporate spin-orbit coupling and noncollinear magnetism. An interface-resolved analysis of the electronic structure reveals that the low-energy states retain a dominant Bi/Se p-orbital character and remain strongly localized near the interface. Mapping the direct band gap in the vicinity of the Γ point identifies an exchange-induced gap of 31.7 meV, indicating the formation of a massive Dirac surface state. Constant-energy spin-texture calculations further demonstrate that the characteristic helical spin-momentum locking is preserved, with a well-defined chirality, despite the presence of the magnetic gap. These findings show that magnetic proximity at the CrI₃/Bi₂Se₃ interface provides an effective platform for the controlled engineering of magnetically gapped topological surface states.