Janus S-XSSe: a new family of 2D polar half-metals with stacking-engineered magnetism and antiferromagnetic spin splitting

The quest for materials uniting polarity with metallicity or half-metallicity is pivotal for next-generation multifunctional devices, yet their realization, particularly with robust magnetism, remains a formidable challenge. Here, we unveil a new family of two-dimensional (2D) Janus S-XSSe (X = Re, Os, V, Cr and Mo) monolayers as intrinsically polar metals/half-metals, exhibiting substantial out-of-plane polarization (2.56–4.00 pC m⁻¹) and excellent structural stability. We demonstrate that S-VSSe, S-CrSSe and S-MoSSe are polar half-metals, where the distinct origins of polarity (S–Se electronegativity difference) and half-metallicity (transition metal d-orbitals) enable their robust coexistence. Furthermore, intriguing anisotropic Rashba effects have been observed in polarized metallic S-ReSSe and S-OsSSe monolayers. In addition, we identify a viable polarization switching pathway, whose energy barrier can be effectively tuned by biaxial strain. Moreover, bilayer S-XSSe systems exhibit enhanced magnetic transition temperature and stacking-dependent magnetism, elucidated via spin Hamiltonian analysis and interlayer electron hopping. Remarkably, an interlayer antiferromagnetic S-VSSe bilayer with parallel polar stacking exhibits significant spin splitting alongside nontrivial topological characteristics, a direct consequence of the built-in electric field breaking inversion symmetry. This discovery of a novel class of polar metals/half-metals, particularly the emergent antiferromagnetic spintronic phenomena in bilayers, paves the way for innovative spintronic and multifunctional electronic applications.