A first-principles study on the effects of 3d transition metal dopants on the valleytronic properties of Janus-type 2H-MoSeTe monolayers

Valleytronics, a promising field in information technology, utilizes the valley degree of freedom for information storage and processing. Two-dimensional (2D) Janus-type transition metal dichalcogenides (TMDs), such as 2H-MoSeTe, are highly attractive for valleytronics due to their structural asymmetry and significant spin-orbit coupling (SOC). However, the valley splitting in pristine Janus TMDs is limited. Here, we employ first-principles calculations to explore the impact of doping Janus 2H-MoSeTe monolayers with 3d transition metals (Mn, Cr, Fe, Co, and Ni) on their valleytronic properties. Our results show that the doped systems exhibit thermodynamic stability and a ferromagnetic ground state with a perpendicular magnetization easy axis. The introduced impurity levels from the dopants' d orbitals hybridize with the host Mo atoms' d orbitals, effectively lifting the <i>K</i>/<i>K</i>' valley degeneracy. Notably, Mn, Fe, and Cr doping induces significant valley splitting of -141 meV, 119 meV, and 105 meV, respectively, underscoring the importance of symmetry breaking and electronic structure changes. The doped systems also display a pronounced Berry curvature with opposite signs at the <i>K</i> and <i>K</i>' valleys, strongly supporting the anomalous valley Hall effect (AVHE). This work provides a deeper understanding of valleytronics in 2D materials and offers a theoretical foundation for designing next-generation spin-valley-coupled electronic and optoelectronic devices.