Observation of strong valley magnetic response in monolayer transition metal dichalcogenide alloys of Mo_0.5W_0.5Se₂ and Mo_0.5W_0.5Se₂/WS₂ heterostructure

Monolayer (1L) transition metal dichalcogenide (TMD) alloys have emerged as a new material system towards future applications for electronic, optoelectronic and spintronic devices. Particularly, the unique valley physics associated with valley polarization and Zeeman effect opens new opportunities for valleytronic applications. However, valley magnetic response in 1L TMD alloys largely remains unexplored. Here, we report strong valley magnetic response of trions in Mo_0.5W_0.5Se₂ and Mo_0.5W_0.5Se₂/WS₂ heterostructures investigated by cryogenic magneto-photoluminescence microspectroscopy. The large g-factors have been extracted for Mo_0.5W_0.5Se₂ and Mo_0.5W_0.5Se₂/WS₂, respectively, which are attributed to the significant impact of strong Coulomb interactions on the trion emission under a perpendicular magnetic field. The reduction of the valley Zeeman splitting in the heterostructure of Mo_0.5W_0.5Se₂/WS₂ is explained in terms of the doping variation caused by the interlayer charge transfer between Mo_0.5W_0.5Se₂ and WS₂, which agrees well with our density functional theory calculations of the band alignment in the Mo_0.5W_0.5Se₂/WS₂ heterostructure. Our findings give new insights into the optical properties of 1L TMD alloys and the interlayer coupling and shed light on the valleytronics.