Seminarium Fizyki Ciała Stałego

Transition metal dichalcogenides (TMDs) and their alloys are promising semiconductor materials that exhibit strong spin–valley coupling and pronounced excitonic effects. Among magnetic van der Waals (vdW) materials, chromium sulfide bromide (CrSBr) has attracted considerable attention as an air-stable, A-type antiferromagnetic semiconductor, owing to its intrinsically coupled magnetic and optical properties. In particular, vdW heterostructures combining twodimensional (2D) TMDs with magnetic materials such as CrSBr provide an exciting platform for engineering the valley and excitonic properties of nonmagnetic TMDs through magnetic proximity effects and interlayer interactions. In this seminar, we will present our recent investigations into the optical and magneto-optical properties of monolayer (ML) TMD alloys and ML TMD/CrSBr heterostructures under different magnetic-field orientations. First, we discuss the influence of alloy disorder on the lowtemperature photoluminescence (PL) and magneto-PL properties of hexagonal boron nitride (hBN)-encapsulated ML Mo₀.₅W₀.₅Se₂. Our results reveal multiple narrow emission peaks with different g-factors, which we attribute to exciton localization induced by the compositional disorder potential. We then explore the optical response of ML TMD/CrSBr heterostructures, where we observe a pronounced influence of the magnetic order in CrSBr on the optical and magneto-optical properties of the monolayer TMDs. These effects include anomalous linear-polarization dependence, unusual variations in exciton and trion energies, and unconventional magneticfield dependence of the PL intensity. Under out-of-plane magnetic fields, we further observe unusual circular-polarization degrees and valley g-factor values, providing clear signatures of asymmetric magnetic proximity exchange interactions and interlayer energy-transfer processes. These observations are discussed in terms of asymmetric magnetic proximity effects, spinselective charge transfer, resonant energy transfer, and possible contributions from exciton/trion–magnon coupling and dielectric anomalies in CrSBr. Overall, our findings highlight the potential of ML TMD alloys and vdW heterostructures incorporating antiferromagnetic–nonmagnetic interfaces as versatile platforms for controlling and engineering the optical, spin, and valley degrees of freedom in 2D semiconductors. These systems offer promising opportunities for the development of next-generation opto-spintronic devices and quantum technologies.